copyright check: Skip auto-generated CMakeFiles

This is needed when building in the source tree.

Fixes google#412

Author: dneto0

utils/add_copyright.py

@@ -63,7 +63,8 @@ def find(top, filename_glob, skip_glob_list):
 def filtered_descendants(glob):
     """Returns glob-matching filenames under the current directory, but skips
     some irrelevant paths."""
-    return find('.', glob, ['third_party', 'ext', 'build*', 'out*'])
+    return find('.', glob, ['third_party', 'external', 'build*', 'out*',
+                            'CompilerIdCXX'])
 
 
 def skip(line):