So in honour of the release of 5.1.10, I decided to take a serious crack at making a guide to compiling Allegro (5.1.10) for Android, on Linux (Xubuntu)...
(Android tested on a MotoG 4.4.2 and Nexus 7 5.1.1)

Anyway I installed a completely clean 14.04 Xubuntu and git'd Allegro, and compiled it for Linux as per the instructions with no problems whatsoever.
(as an initial test just to make sure everything worked before moving onto the
Android build)

Then it came to making the Android build, and here is what I found...
the following dependencies were claimed to be not found on a fresh cmake of the Allegro build
OpenGL, OpenAL, FLAC, DUMB, OGG, Vorbis, Theora, Freetype, PhysFS, PKG_CONFIG

As it found all of the OpenGLES stuff without error, I assumed (rightly or wrongly?) that the OpenGL missing libraries weren't needed for the Android build?

For the missing PKG_CONFIG_EXECUTABLE I pointed the make file to the pkgconfig included with the ndk at
$HOME/android-ndk/prebuilt/linux-x86_64/lib

Compiling OpenAL (using version1.16.0, as 1.15.1 fails to build) as per this site
how-to-build-for-arm.wikispaces.com/openalsoft
It builds fine with no errors, however Allegro's cmake file doesn't find the include directory, but adding $HOME/allegro/build/deps/include/AL seems to work (A similar workaround is need for both the ft2build and freetype2 file directories in the cmake file, as it is installed at $HOME/allegro/build/deps/include/freetype2 but isn't found.)
Allegro compiles fine, but it then crashes if you try any of the demos.

I found the same is also true for flac-1.3.1 despite it cross compiling fine, with
./configure --host=arm-linux-androideabi --prefix=$Home/allegro/build/deps
and Allegro compiles fine, (cmake finds the include/lib), but causes crashes on starting the demos.

However OGG (1.3.2) seems to be fine, compiling exactly the same way as above.

LibVorbis (1.3.5) compiles fine as above, but when the Allegro cmakes file runs it says that it fails on the LibVorbis compile test.
CMakeError.log reports an error
$HOME/allegro/build/deps/lib/libvorbisfile.a: no archive symbol table (run ranlib)
$HOME/allegro/build/deps/lib/libvorb.a: no archive symbol table (run ranlib)
producing an error as an undefined reference to 'ov_info' in the next line

LibTheora (1.1.1) gives me a error trying to cross compile it -
checking host system type... Invalid configuration 'arm-linux-androideabi': system 'androideabi' not recognised

Freetype2 seems to build fine, without error, and builds fine with Allegro-Android, with no reported crashes thus far. I used the instructions as per the
how-to-build-for-arm.wikispaces.com/freetype2
Although, as mentioned above, I had to manually add the freetype2 include directory to the Allegro make file.

I haven't been able to figure out thus far how to cross compile PhysFS or DUMB.

(EDIT) I found this link so will try and cross compile PhysFS later and see if it works,
libphysfs-android-master.zip
(from: github.com/sam101/libphysfs-android)

I don't know whether to feel elated at having achieved something, and despondent at getting so little progress after three days, especially as I managed to get OpenAL, FLAC and Vorbis (but not FreeType2) to compile on an earlier version of Allegro about 18months (don't ask me how, I have forgotten, hence why I wanted also to preserve this "quest" in stone for future adventurers).

Any help would be greatly appreciated.

Well I just tried the physFS link we both put up above. And after commenting out the lines 268 and 270 with the lastDirectory variables, in wad.c, (these caused a compile error as it was "set but unused", and setting the compiler flags in the cmake file to -Wno-error didn't help), it compiled without complaint. I also manually added the $HOME/allegro/build/deps to the PREFIX_INSTALL option in the make file.
I ran the Allegro make file, and it found the physFS fine. However when I ran the "sudo make" commanded the build failed at linking liballegro_physfs-debug.so which it says is an incompatable target.

Thanks for your kind words, its nice to know I am not the only one, as sometimes I just think I am really stupid for not being able to figure this out.

Yeah I didn't have any problem with compiling Allegro-android without dependencies "out of the box", which was nice.

Good news, after playing around some more, and deepening my knowledge of cmake/cross compiling I managed to get physFS to cross compile from the link above.

I had to turn off/comment out CD-Rom Support in the CMakeLists.txt file. This is because when I tried to cross compile it would throw an exception saying that there were undefined references to a couple of function calls from mntent.h
I also had to set the C compiler flag as noted above to -Wno-error due to the warning about the lastDirectory variable in wad.c (see above)

Here is the cmake command I used incase it helps anyone else:-
cmake .. -DC_MAKE_SYSTEM_NAME=Linux -DCMAKE_SYSTEM_VERSION=1 -DCMAKE_C_COMPILER=$HOME/android-toolchain/arm-linux-androideabi-gcc -DCMAKE_CXX_COMPILER=$HOME/android-toolchain/arm-linux-androideabi-g++ -DCMAKE_FIND_ROOT_PATH=$HOME/android-toolchain -DCMAKE_INSTALL_PREFIX=$HOME/allegro/build/deps

(Edit) Some more success of a sort, I can get Vorbis to cross-compile and build with Allegro without complaint now, but it crashes the examples. :/

Success - I can compile and build with the Vorbis dependency.
(What I was doing from was forgetting to use the LDFLAGS=avoid-version on the make and make install when cross compiling.)

Off to try the same with the FLAC and THEORA cross compiles.

(Edit FLAC) Okay I can get Flac to cross-compile (both 1.2 and 1.3) and neither these,
nor the precompiled binaries that SCUMMVM.org offer work with the ALLEGRO build, they failed the Performing Test FLAC_COMPILES - Failed -
with
/home/yodhe/allegro/build/deps/lib/libFLAC.a(fixed.o):fixed.c:function FLAC__fixed_compute_best_predictor: error: undefined reference to 'log'
/home/yodhe/allegro/build/deps/lib/libFLAC.a(fixed.o):fixed.c:function FLAC__fixed_compute_best_predictor: error: undefined reference to 'log'
/home/yodhe/allegro/build/deps/lib/libFLAC.a(fixed.o):fixed.c:function FLAC__fixed_compute_best_predictor: error: undefined reference to 'log'
/home/yodhe/allegro/build/deps/lib/libFLAC.a(fixed.o):fixed.c:function FLAC__fixed_compute_best_predictor: error: undefined reference to 'log'
/home/yodhe/allegro/build/deps/lib/libFLAC.a(lpc.o):lpc.c:function FLAC__lpc_quantize_coefficients: error: undefined reference to 'frexp'
/home/yodhe/allegro/build/deps/lib/libFLAC.a(lpc.o):lpc.c:function FLAC__lpc_quantize_coefficients: error: undefined reference to 'lround'
/home/yodhe/allegro/build/deps/lib/libFLAC.a(lpc.o):lpc.c:function FLAC__lpc_quantize_coefficients: error: undefined reference to 'lround'
/home/yodhe/allegro/build/deps/lib/libFLAC.a(lpc.o):lpc.c:function FLAC__lpc_quantize_coefficients: error: undefined reference to 'lround'
/home/yodhe/allegro/build/deps/lib/libFLAC.a(lpc.o):lpc.c:function FLAC__lpc_quantize_coefficients: error: undefined reference to 'lround'

(Edit THEORA) No luck with THEORA either, after playing around it flips out during the cross compile make with a
error: .libs/bitpack.o: incompatible target

(Edit OpenAL) The problem with OpenAl is that the linker seems to be ignoring the LDFLAGS=-avoid-version, so it is created libraries with the .so.1 and so.16.0 extensions as well, which then cause an exception from inside the Android Allegro build at runtime, as the libraries should only be .so, with no version number.
I fixed this by edits the CMakeList.txt and setting the variable to STATIC instead of SHARED. I must be getting tired making such silly mistakes, so night all till another time.
Unfortunately OpenAL still crashes as runtime, with the following error..
: java.lang.UnsatisfiedLinkError: dlopen failed: cannot locate symbol "LookupUIntMapKey" referenced by "liballegro_audio-debug.so"...

(Edit OGG is borked for Android 5+)
OGG does not work and causes a runtime exception crash it you attempt to use libogg with Android 5+
the error is below:
I/DEBUG ( 122): pid: 12208, tid: 12232, name: trampoline >>> org.liballeg.examples.cosmic_protector <<<
I/DEBUG ( 122): signal 6 (SIGABRT), code -6 (SI_TKILL), fault addr --------
I/DEBUG ( 122): Abort message: 'art/runtime/check_jni.cc:65] JNI DETECTED ERROR IN APPLICATION: native code passing in reference to invalid local reference: 0x100005'
I/DEBUG ( 122): r0 00000000 r1 00002fc8 r2 00000006 r3 00000000
I/DEBUG ( 122): r4 6ae9cdd8 r5 00000006 r6 0000000b r7 0000010c
I/DEBUG ( 122): r8 00000000 r9 400769f8 sl 68de6270 fp 0000058c
I/DEBUG ( 122): ip 00002fc8 sp 6ae9c798 lr 4013ac81 pc 40160c04 cpsr 60070010
I/DEBUG ( 122):
I/DEBUG ( 122): backtrace:
I/DEBUG ( 122): #00 pc 0003cc04 /system/lib/libc.so (tgkill+12)
I/DEBUG ( 122): #01 pc 00016c7d /system/lib/libc.so (pthread_kill+52)
I/DEBUG ( 122): #02 pc 0001789b /system/lib/libc.so (raise+10)
I/DEBUG ( 122): #03 pc 00014029 /system/lib/libc.so
I/DEBUG ( 122): #04 pc 000124f0 /system/lib/libc.so (abort+4)
I/DEBUG ( 122): #05 pc 00218341 /system/lib/libart.so (art::Runtime::Abort()+160)
I/DEBUG ( 122): #06 pc 000a6eeb /system/lib/libart.so (art::LogMessage::~LogMessage()+1322)
I/DEBUG ( 122): #07 pc 000b0bf9 /system/lib/libart.so
I/DEBUG ( 122): #08 pc 000b1151 /system/lib/libart.so (art::JniAbortF(char const*, char const*, ...)+60)
I/DEBUG ( 122): #09 pc 000b3509 /system/lib/libart.so
I/DEBUG ( 122): #10 pc 000b63f1 /system/lib/libart.so
I/DEBUG ( 122): #11 pc 000a65dd /data/app/org.liballeg.examples.cosmic_protector-1/lib/arm/liballegro-debug.so

Now this combined with the lround and log functions missing from FLAC compile crash and I am beginning to suspect due to the changes in how android deals with some libraries as can be seen in this thread
https://groups.google.com/forum/#!topic/android-ndk/RjO9WmG9pfE

I tried an older NDK, (r9c v r10e) and no joy.
Infact now I have gone seemingly backwards, and have lost audio.
I hope I am right in thinking that I shouldn't need any dependency other than opensl for basic audio functions?
So I reinstalled with Xubuntu 15.04 as a fresh install (after updating from 14.04), and apart from a whole skew of cmake warnings about cmake_policy 00026 and not using targets as locations (Cmake 3.0+, and got rid of by adding a cmake_policy 00026 OLD below the other cmake_policy statement in the CMakeLists.txt), whilst it finds Opensl and claims to compile the audio and acodec libraries, it won't build the audio examples and there is no audio on the demos (which previously I had managed to get on a vanilla android build), except for "speed".
I've tried API 21, 19 and 15 with the same results.
This is all from a fresh installs of both 14.04 and 15.04 Xubuntu.
(EDIT - reverting to cmake 2.8.8 makes no difference)

This is my Allegro Android build from a fresh Xubuntu install following the instructions.
As you can see OpenSl is found, but the allegro_audio (and allegro_acodec) library and consequently the audio examples aren't built
This is for API 15, but I get the same regardless with 19, 21, and ndk-r9c and either Xubuntu 14.04/15.04, and either Cmake 2.8 or 3+.
Tested on both 4.4.2 and 5.1 Android OS.

And FYI Allegro Linux compiles/builds perfectly and all works including audio.
I tried Allegro 5.1.9 it made no difference.

EDIT - Okay I just spend an hour doing an sdk/ndk/allegro install on my other linux machine to check if it was a hardware configuration error or something as arcane.
IT ISN'T. I am getting exactly the same results on my 32bit Xubuntu 14.04 machine as well.

sitting in the corner with 'D' hat on

My mistake, it was compiling allegro_audio and allegro_acodec in the vanilla build, it just wasn't listing them alongside the other libraries at the end of the cmake build output, when it says
-- Not building tests due to missing library. Have: allegro allegro_main allegro_image allegro_color allegro_font allegro_primitives

Also it turns out the skater and cosmic protector don't have sound until I compile and build allegro with ogg AND vorbis. That will teach me to NOT have the great idea to turn off the examples to speed up the build times.

Anyway OpenAl still crashes with that LookUpUInt, though I am going to have a go a adding that function to the source to see if it makes a difference, as it seems to be a function in older OpenAl versions.

Thanks, and I'm back to getting the other dependencies to play nice.

EDIT Still getting the same errors with FLAC, though 1.2.1 produces only missing "log" function rather than 1.3.1 with "log and lround" missing.

FLAC seems to test compile successfully now, but Allegro won't build after I re-git'd it.

I have to sudo everything now, such as mkdir build, etc, and then it keeps saying android-tool not found when I cmake it, regardless of what export PATH i do.