Update from https://crrev.com/329939

tools/clang/plugins/tests/test.sh

 #!/bin/bash
 #
 # Copyright (c) 2011 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 #
 # Hacky, primitive testing: This runs the style plugin for a set of input files
 # and compares the output with golden result files.
 
 E_BADARGS=65
@@ skipping 13 matching lines @@
   echo ""
 }
 
 # Runs a single test case.
 do_testcase() {
   local flags=""
   if [ -e "${3}" ]; then
     flags="$(cat "${3}")"
   fi
 
-  if [ "$(uname -s)" = "Darwin" ]; then
-    flags="${flags} -isysroot $(xcrun --show-sdk-path) -stdlib=libstdc++"
+  # TODO(thakis): Remove once the tests are standalone, http://crbug.com/486559
+  if [[ "$(uname -s)" == "Darwin" ]]; then
+    flags="${flags} -isysroot $(xcrun --show-sdk-path)"
+  fi
+  if [[ "$(uname -s)" == "Darwin" && "${flags}" != *-target* ]]; then
+    flags="${flags} -stdlib=libstdc++"
   fi
 
   flags="${flags} -Xclang -plugin-arg-find-bad-constructs \
       -Xclang with-ast-visitor"
 
   local output="$("${CLANG_PATH}" -fsyntax-only -Wno-c++11-extensions \
       -Wno-inconsistent-missing-override \
       -isystem ${THIS_DIR}/system \
       -Xclang -load -Xclang "${PLUGIN_PATH}" \
       -Xclang -add-plugin -Xclang find-bad-constructs ${flags} ${1} 2>&1)"
@@ skipping 45 matching lines @@
   do_testcase "${input}" "${input%cpp}txt" "${input%cpp}flags"
 done
 
 for input in *.c; do
   do_testcase "${input}" "${input%c}txt" "${input%c}flags"
 done
 
 if [[ "${failed_any_test}" ]]; then
   exit ${E_FAILEDTEST}
 fi