[clang][test] Fix -DBUILD_SHARED_LIBS build by adding depency on MC from clangTesting

Commit 34de7da6 (D143436) introduced a
dependency on the TargetRegistry in `getAnyTargetForTesting`. This is
part of MC, which wasn't listed in clang/lib/Testing/CMakeLists.txt.
This broke the -DBUILD_SHARED_LIBS=True builds.