Index: llvm/utils/gn/build/write_cmake_config.py
===================================================================
--- llvm/utils/gn/build/write_cmake_config.py
+++ llvm/utils/gn/build/write_cmake_config.py
@@ -101,6 +101,7 @@
 
     if not os.path.exists(args.output) or open(args.output).read() != output:
         open(args.output, 'w').write(output)
+        os.chmod(args.output, os.stat(args.input).st_mode & 0777)
 
 
 if __name__ == '__main__':