Require a shell for this test.

Some versions of python will expand the glob used in the test, others wont,
causing the test to fail when run with LIT_USE_INTERNAL_SHELL=1.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@185653 91177308-0d34-0410-b5e6-96231b3b80d8