diff --git a/libcxx/utils/libcxx/test/format.py b/libcxx/utils/libcxx/test/format.py
--- a/libcxx/utils/libcxx/test/format.py
+++ b/libcxx/utils/libcxx/test/format.py
@@ -6,6 +6,7 @@
 #
 #===----------------------------------------------------------------------===##
 
+from libcxx.test.dsl import *
 import lit
 import lit.formats
 import os
@@ -21,12 +22,7 @@
     This is done by checking whether the %{cxx} substitution in that
     configuration supports certain compiler flags.
     """
-    command = "%{{cxx}} -xc++ {} -Werror -fsyntax-only -Xclang -verify-ignore-unexpected".format(os.devnull)
-    command = lit.TestRunner.applySubstitutions([command], config.substitutions,
-                                                recursion_limit=config.recursiveExpansionLimit)[0]
-    devNull = open(os.devnull, 'w')
-    result = subprocess.call(command, shell=True, stdout=devNull, stderr=devNull)
-    return result == 0
+    return hasCompileFlag(config, '-Xclang -verify-ignore-unexpected')
 
 def _getTempPaths(test):
     """