Sidestep false positive due to a matching git repository name

I have failures in this test because the grep @b gets confused by the
clang version including a repository name like this

!1 = !{!"clang version 10.0.0 (git@build-machine:llvm/llvm-monorepo.git fe958c0e8c89ec663c8e551936778e2cbb460154)"}

I considered something like grep -w but my understanding of the manpages
was that that isn't super portable. So I think it is easier to make
clang not to output that metadata using -fno-ident.

Differential Revision: https://reviews.llvm.org/D65635

llvm-svn: 367826