Ignore "build" dirs in check_path_lengths. (iree-org#17562)

These are produced by `python -m pip wheel compiler/` and are already
ignored by .gitignore.

Progress on iree-org#17430

skip-ci: lint-only change

build_tools/scripts/check_path_lengths.py

@@ -67,6 +67,9 @@ def main(args):
         # object files or binaries that could trip up the build system.
         if not args.include_tests and "test" in dirnames:
             dirnames.remove("test")
+        # Skip build directories (should really anything be covered by .gitignore).
+        if "build" in dirnames:
+            dirnames.remove("build")
 
         path = pathlib.Path(dirpath).relative_to(repo_root).as_posix()
         if len(path) > args.limit: