guard multiprocessing code with main (#31992)

* guard multiprocessing code with main

* Update fix_build_deps.py

* merge last master

* add back execution bit to fix_build_deps

Co-authored-by: AJ Heller <hork@google.com>

tools/distrib/fix_build_deps.py

@@ -640,7 +640,7 @@ def make_library(library):
     return (library, error, deps, external_deps)
 
 
-if __name__ == "__main__":
+def main() -> None:
     update_libraries = []
     for library in sorted(consumes.keys()):
         if library in no_update:
@@ -663,3 +663,7 @@ if __name__ == "__main__":
 
     if error:
         sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()