Print each clang-tidy command and its output under a lock

This fixes NUL bytes and lost lines in the output of run_O2CodeChecker.py.

- All threads wrote to sys.stdout concurrently, which corrupts it with Python 3.9/3.10.
- With a fake clang-tidy, 20000 files at -j 64 gave ~200k NUL bytes and ~2000 lost lines with Python 3.10.
- Each thread now captures the clang-tidy output and prints it with the command line under a lock.

alisw/alidist#6360

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Print each clang-tidy command and its output under a lock

This fixes NUL bytes and lost lines in the output of run_O2CodeChecker.py.

- All threads wrote to sys.stdout concurrently, which corrupts it with Python 3.9/3.10.
- With a fake clang-tidy, 20000 files at -j 64 gave ~200k NUL bytes and ~2000 lost lines with Python 3.10.
- Each thread now captures the clang-tidy output and prints it with the command line under a lock.

alisw/alidist#6360

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
(cherry picked from commit 40c1855)

Fix to work with Clang 22

Make compatible to CMake 4

Handle case in which -extra-args has more than one extra arg.

Update to the Clang v20.1.7 version of the main

Also make sure we build only the plugin, since the upstream
clang now supports loading clang-tidy plugins via the -load
option.

Use Clang provided public API

- Drop our own private copy of the headers
- Use the CMake Config

***

Support OMP

Merge pull request #42 from davidrohr/PR

Add -extra-args option

Bump to LLVM 18.1.8