Fix warnings in test/std/language.support

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@242624 91177308-0d34-0410-b5e6-96231b3b80d8

test/libcxx/compiler.py

@@ -150,3 +150,14 @@ class CXXCompiler(object):
         cmd, out, err, rc = self.compile(os.devnull, out=os.devnull,
                                          flags=flags)
         return rc == 0
+
+    def addCompileFlagIfSupported(self, flag):
+        if isinstance(flag, list):
+            flags = list(flag)
+        else:
+            flags = [flag]
+        if self.hasCompileFlag(flags):
+            self.compile_flags += flags
+            return True
+        else:
+            return False