This PR fixes the "unassigned file number" error in llvm-mca when
processing GCC-generated assembly with debug information #6795 .
**Problem**: GCC with `-g` flag generates `.loc` and `.file` debug
directives that cause llvm-mca to fail with "unassigned file number"
errors.
**Solution**: Filter out `.loc` and `.file` directives during assembly
preprocessing, similar to how other problematic directives are already
handled.
**Changes**:
- Add regex filtering for `.loc` and `.file` directives in
`rewriteAsm()`
- Make `rewriteAsm()` method public for testability
- Add comprehensive test coverage for debug directive removal
The fix is minimal, targeted, and follows the existing pattern of
directive filtering.
c7056b31eb