[AArch64] Add AArch64 Neon intrinsics test produced by emperor

The test has a basic correctness check for every AArch64 Neon intrinsic,
except for a small number of intrinsics that emperor currently doesn't support
yet.

This adds a new sub-directory SingleSource/UnitTests/Vector/AArch64, as there
wasn’t a sub-directory yet for AArch64-specific test cases.

llvm-svn: 221255
4 files changed