perf python: Clean up and restructure setup.py

Clean up and restructure the python setup script to resolve pylint
warnings, improve code quality, and increase robustness and
readability, targeting Python 3.9+ (the Linux kernel build minimum
Python version).

Changes:
- Restructure the script to use a `main()` function as the entry point,
  leaving only imports, classes, and pure functions at module level.
- Eliminate all global/module-level variables, making them local to
  `main()` or the respective classes/functions.
- Make `clang_has_option` a pure function by passing all necessary
  parameters explicitly.
- Extract clang compiler flag filtering into a new
  `filter_clang_options` helper function. This function uses a loop
  over a tuple of options, replacing ~30 lines of repetitive blocks
  and reducing branch/statement complexity in the main flow.
- Cleanly define attributes in `__init__` for `BuildExt` and
  `InstallLib` and read environment variables dynamically within the
  methods (including `srctree` in `InstallLib.run`), removing their
  dependency on global variables.
- Replace legacy Popen with subprocess.run for safer process handling.
- Use quote-aware flag filtering (`shlex.split`, filter, `shlex.join`)
  on sysconfig CFLAGS and OPT instead of regex `re.sub` substitutions.
  This avoids boundary bugs and safely handles quoted arguments and
  options with values.
- Rely on setuptools to handle user CFLAGS from the environment
  directly rather than manually prepending them to extra_compile_args.
- Safely parse `CC` env var using `shlex.split` to handle quotes and
  pass compiler arguments as `list[str]` lists to helper functions,
  avoiding redundant string formatting and parsing.
- Remove unused `import re`.
- Rename setuptools command subclasses to PascalCase (BuildExt,
  InstallLib).
- Add type annotations to functions and methods.
- Add missing docstrings for module, functions, and classes.
- Split long lines to adhere to standard limits.

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

0 files changed, 0 insertions, 0 deletions