Preemptively disable unsigned integer sanitization in 32 and 64 bit versions...

Preemptively disable unsigned integer sanitization in 32 and 64 bit versions of __murmur2_or_cityhash. This lets people use the unsigned integer overflow checker in UBSAN w/o getting hits from libc++'s hash code (where the unsigned integer overflow is legal and deliberate)> Patch by @danielaustin. Reviewed as: http://reviews.llvm.org/D15973

llvm-svn: 257368