don't use pyc files during image build

Author: timfel

graalpython/lib-python/3/importlib/_bootstrap_external.py

@@ -312,6 +312,8 @@ def cache_from_source(path, debug_override=None, *, optimization=None):
     If sys.implementation.cache_tag is None then NotImplementedError is raised.
 
     """
+    if __graalpython__.in_image_buildtime:
+        return
     if debug_override is not None:
         _warnings.warn('the debug_override parameter is deprecated; use '
                        "'optimization' instead", DeprecationWarning)