ARM64: enable aarch64-neon-intrinsics.c test

This adds support for the various NEON intrinsics used by
aarch64-neon-intrinsics.c (originally written for AArch64) and enables the
test.

My implementations are designed to be semantically correct, the actual code
quality looks like its a wash between the two backends, and is frequently
different (hence the large number of CHECK changes).

llvm-svn: 205210