[msan] allow -fsanitize-coverage=N together with -fsanitize=memory, clang part

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@223311 91177308-0d34-0410-b5e6-96231b3b80d8
Implement __umulh with __int128 arithmetic

Use the same approach as _umul128, but just return the high half.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@223316 91177308-0d34-0410-b5e6-96231b3b80d8
Add test for __umulh

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@223319 91177308-0d34-0410-b5e6-96231b3b80d8