Fixing warnings for unused variables and copy ellision

Summary:
The std::move was preventing copy ellision when compiled with
clang, the patch fixes the warning along with rearranging code
to remove unused variables warnings on Linux machines with
older perf_event interface.

Reviewers: labath, ted

Reviewed By: labath

Differential Revision: https://reviews.llvm.org/D34946

llvm-svn: 307030