The $(gnt_python_sbin_SCRIPTS) are GENERATED_FILES

Before the layout change, the corresponding scripts used to be
part of PYTHON_BOOTSTRAP, hence were already considered as
generated.
Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Thomas Thrainer <thomasth@google.com>
Reviewed-by: Michele Tartara <mtartara@google.com>

Makefile.am

@@ -276,7 +276,8 @@ CLEANFILES = \
 GENERATED_FILES = \
 	$(built_base_sources) \
 	$(BUILT_PYTHON_SOURCES) \
-	$(PYTHON_BOOTSTRAP)
+	$(PYTHON_BOOTSTRAP) \
+	$(gnt_python_sbin_SCRIPTS)
 
 HS_GENERATED_FILES =
 if WANT_HTOOLS