[JITLink] Add check to JITLink unit test to bail out for unsupported targets.

This should prevent spurious JITLink unit test failures for builds that do not
support the target(s) required by the tests.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@358825 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed