Fix build failure

Author: jmschonfeld

Tests/Functional/lit.cfg

@@ -99,7 +99,7 @@ else:
         '-L', os.path.join(foundation_dir, 'lib'),
         '-I', foundation_dir,
         '-I', os.path.join(foundation_dir, 'swift'),
-        '-I', os.path.join(foundation_dir, '_CModulesForClients',
+        '-I', os.path.join(foundation_dir, '_CModulesForClients'),
         '-Xcc', '-F', '-Xcc', foundation_dir,
     ])