[msan] Fix gethostbyname_r and similar interceptors.

*h_errno is written not on success, but on failure.
In fact, it seems like it can be written even when return value signals
success, so we just unpoison it in all cases.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@197383 91177308-0d34-0410-b5e6-96231b3b80d8