[msan] Intercept __strto*_internal.

This should fix strtoimax/strtoumax on newer glibc.
https://code.google.com/p/memory-sanitizer/issues/detail?id=36


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@210463 91177308-0d34-0410-b5e6-96231b3b80d8