Tools/run-clang-tidy: add -exclude argument for file filtering

Add regex-based file exclusion to the clang-tidy runner script.
This allows excluding paths (submodules, vendored code, tests) from
static analysis without modifying .clang-tidy files in each directory.

The -exclude argument accepts a regex pattern that is matched against
file paths from the compilation database. Matching files are skipped.

Example: -exclude="src/lib/foo|src/modules/bar"

This prepares for the clang-tidy v6 to v18 migration where we need
to exclude external code that we consume but don't maintain.

Signed-off-by: Ramon Roche <mrpollo@gmail.com>

Tools/run-clang-tidy.py

@@ -144,6 +144,8 @@ def main():
                       help='number of tidy instances to be run in parallel.')
   parser.add_argument('files', nargs='*', default=['.*'],
                       help='files to be processed (regex on path)')
+  parser.add_argument('-exclude', dest='exclude', default=None,
+                      help='regular expression matching files to exclude')
   parser.add_argument('-fix', action='store_true', help='apply fix-its')
   parser.add_argument('-format', action='store_true', help='Reformat code '
                       'after applying fixes')
@@ -192,6 +194,7 @@ def main():
 
   # Build up a big regexy filter from all command line arguments.
   file_name_re = re.compile('(' + ')|('.join(args.files) + ')')
+  exclude_re = re.compile(args.exclude) if args.exclude else None
 
   try:
     # Spin up a bunch of tidy-launching threads.
@@ -205,6 +208,8 @@ def main():
     # Fill the queue with files.
     for name in files:
       if file_name_re.search(name):
+        if exclude_re and exclude_re.search(name):
+          continue
         queue.put(name)
 
     # Wait for all threads to be done.