[libomptaret][test] Announce compiler features

This is a follow-up to r341371: The new test for PR38704 doesn't
work with Clang 6.0. It uses an UNSUPPORTED: clang-6, but that
hasn't worked because the compiler features weren't known to lit.

git-svn-id: https://llvm.org/svn/llvm-project/openmp/trunk@341448 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed