do not register matcher for objc-only checks when analyzing non-objc sources to save resources

Summary: I did not put lang opt check in AvoidSpinlockCheck since OSSpinLock is not objc specific. We won't want to skip it when analyzing some C++ target used by other ObjC sources.

Reviewers: hokein, benhamilton

Reviewed By: benhamilton

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D44174

llvm-svn: 326928