ci: turn the Android x86 job back on

[WizzardSK]

android-x86 is the one ABI commented out in .gitlab-ci.yml, and it builds today. Uncommenting it is the whole change.

I ran it on a GitHub runner with the same platform=android-x86 line the other three ABIs use, NDK 29.0.14206865, TARGET=mame SUBTARGET=arcade:

clang++ -o ../../../../../mamearcade_libretro_android.so ... --target=i686-none-linux-android24 ...
-rwxr-xr-x 1 runner runner 249255316 mamearcade_libretro_android.so
mamearcade_libretro_android.so: ELF 32-bit LSB shared object, Intel 80386, version 1 (SYSV), dynamically linked, stripped

Nothing else needed touching — no source changes, no flags beyond what the android-make template already passes. 32-bit is not a problem for this tree in general either: linux-i686, windows-i686 and android-armeabi-v7a are all active and green.

I have not run it on the buildbot's own image, so if there is a reason this was switched off that is not "it did not build", I have not seen it — the commit that commented it out would know better than I do.