Support for armv8 arch only devices

[nfynt]

Recent pixel devices do not report armv7 arch support and only arm64-v8a. This causes benchmark test to exit early with message stating "Not an ARMv7 and not an X86 SSSE3 CPU !\n".

This update includes check for ANDROID_CPU_FAMILY_ARM64 along with subsequent cmake and gradle updates for running the test app.

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[DanAlbert]

There's actually quite a lot here that I think can be safely deleted, since Neon is available by default for a few NDK releases now. I'm not totally sure how much I can purge though, so I'll merge this and take a look at the cleanup separately.

For that matter, this whole sample would probably be more useful as a generic vectorization sample rather than specific to Neon, since there are also clang's arch-generic vector APIs, as well as SVE coming up with newer versions of armv8, and whatever rv64 has planned, but that's definitely out of scope for this PR :)

[DanAlbert]

I think you probably need to update

ndk-samples/hello-neon/app/src/main/cpp/helloneon-intrinsics.c

Line 18 in ece52f2

#if defined(HAVE_NEON) && defined(HAVE_NEON_X86)

?

[DanAlbert]

Actually it was the CMakeLists.txt that needed updating. Pushed the fix to your branch.