[llvm] [gcov] Set current_working_directory to . for GCC>=9 (PR #121420)

[Fangrui Song via llvm-commits]

MaskRay wrote:

Abandoned. It has been almost 5 years that llvm-cov supports the gcov format used b GCC 9~11. Just bumped Clang's producer format from 4.8 to 11 (9) and folded this change.

https://github.com/llvm/llvm-project/pull/121420