ANDROID: use arm-linux-androidkernel- for CROSS_COMPILE_COMPAT

While ultimately resulting in the same binary being used, this allows
the arm64 compat vdso to use the same target triple as an ARCH=arm build
for Android.

This means that arm-linux-androideabi-elfedit doesn't need to be created
in: https://android.googlesource.com/platform/prebuilts/gas/linux-x86/

.

Bug: 141693040
Test: BUILD_CONFIG=common/build.config.gki.aarch64 ./build/build.sh
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Change-Id: Iecebbfe2588615399c73255fd89d0c5ce42db9c0