Add GCC codecoverage flags (#43066)
Summary:
Rename `CLANG_CODE_COVERAGE` option to `CODE_COVERAGE` and add compiler specific flags for GCC and Clang
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43066
Reviewed By: scintiller
Differential Revision: D23137488
Pulled By: malfet
fbshipit-source-id: a89570469692f878d84f7da6f9d5dc01df423e80
