diff --git a/llvm/utils/lit/lit/TestingConfig.py b/llvm/utils/lit/lit/TestingConfig.py
--- a/llvm/utils/lit/lit/TestingConfig.py
+++ b/llvm/utils/lit/lit/TestingConfig.py
@@ -58,6 +58,7 @@
             'WindowsSDKLibVersion',
             'SOURCE_DATE_EPOCH',
             'GTEST_FILTER',
+            'DFLTCC',
         ]
 
         if sys.platform == 'win32':