Don't just assume that either uint64_t or u_int64_t is available. Instead,

Don't just assume that either uint64_t or u_int64_t is available. Instead,
give preference to uint64_t if it exists. If not, check for u_int64_t. If
that doesn't exist either, then error out.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16149 91177308-0d34-0410-b5e6-96231b3b80d8