[clang-format] Add ability for clang-format-diff to exit with non-0 status (#70883)

This patch adds the ability for the clang-format-diff script to exit
with a non-zero status if it detects that formatting changes are
necessary. This makes it easier to use clang-format-diff as part of a
DevOps pipeline, since you could add a stage to run clang-format-diff
and fail if the formatting needs to be fixed.

Author: conrad-donahue

clang/tools/clang-format/clang-format-diff.py

@@ -185,6 +185,7 @@ def main():
             diff_string = "".join(diff)
             if len(diff_string) > 0:
                 sys.stdout.write(diff_string)
+                sys.exit(1)
 
 
 if __name__ == "__main__":