[asan] Add "arm64" into the list of 64-bit architectures

It looks like get_bits_for_arch doesn't recognize "arm64" as a 64-bit architecture, and it actually matches the "arm" regexp, which marks it as 32-bit. Let's fix that by matching the 64-bit list first and addin "arm64" into the list.

Differential Revision: https://reviews.llvm.org/D43155

llvm-svn: 325300