Accept GCC warnings without an option suffix #159336

The GCC parser in Tools/build/check_warnings.py accepts a warning without an option suffix in its regular expression, then fails while extracting the absent group. This also occurs with compiler output that omits diagnostic option names.

Reproducer, run with the interpreter built from the CPython checkout:

import sys
sys.path.insert(0, 'Tools/build')
import check_warnings

result = check_warnings.extract_warnings_from_compiler_output(
    'source.c:1:2: warning: example', 'gcc')
print(result)

Expected: The warning is returned with an empty option field.

Observed: The parser reports that it cannot extract the warning and exits with status 1.

Environment: CPython main, Windows debug build.

Linked PRs

• gh-159336: Accept GCC warnings without an option suffix #159337