[benchmark] Fix buildbots failing to identify regex support

This is cleanup after newly introduced google/benchmark library
(rL340809). Many buildbots fail to identify regex engine support, so
this should presumably fix the issue.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@340827 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed