Add no_instrument_function attribute to Objective C methods as well

There are functions where we do not want function instrumentation which is why we have `__attribute__((no_instrument_function))`. Extending this functionality to disable instrumentation for Objective-C methods as well. Objective C methods like `+load` run premain and having instrumentation on them causes runtime errors depending on the implementation of `__cyg_profile_func_enter` etc. functions

Reviewed By: rjmccall, aaron.ballman

Differential Revision: https://reviews.llvm.org/D111286