Android NDK support for x86 and mips

Android NDK support for x86 and mips

This does not do the full toolchain setup like the arm builds. It only
allows for ndk-builds. See the instructions in tests/android/README or
the webm jnin bindings project:
https://chromium.googlesource.com/webm/bindings/+/master/JNI/README.Android

Because this support is not quite polished, the build targets must be
forced. Please use
--force-target=x86-android-gcc --disable-ssse3 --disable-sse4_1 --disable-avx2
--force-target-mips-android-gcc

Change-Id: Ie2b6623f71ac816e3965c39bf97097e9d30b6e94