Convert an OCaml binding grep test to FileCheck

I shaved this yak because I mistakenly thought that this was one of the
last grep tests.  Turns out my search was skipping .ll files, for which
there are ~1200 more tests using grep.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185819 91177308-0d34-0410-b5e6-96231b3b80d8