Update from https://crrev.com/327068

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
 E_FAILEDTEST=1
 
 failed_any_test=
 
+THIS_DIR="$(dirname "${0}")"
+
 # Prints usage information.
 usage() {
   echo "Usage: $(basename "${0}")" \
     "<path to clang>" \
     "<path to plugin>"
   echo ""
   echo "  Runs all the libFindBadConstructs unit tests"
   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++"
   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} ${1} 2>&1)"
   local diffout="$(echo "${output}" | diff - "${2}")"
   if [ "${diffout}" = "" ]; then
     echo "PASS: ${1}"
   else
     failed_any_test=yes
     echo "FAIL: ${1}"
     echo "Output of compiler:"
     echo "${output}"
@@ skipping 23 matching lines @@
   usage
   exit ${E_BADARGS}
 else
   export CLANG_PATH="${1}"
   export PLUGIN_PATH="${2}"
   echo "Using clang ${CLANG_PATH}..."
   echo "Using plugin ${PLUGIN_PATH}..."
 
   # The golden files assume that the cwd is this directory. To make the script
   # work no matter what the cwd is, explicitly cd to there.
-  cd "$(dirname "${0}")"
+  cd "${THIS_DIR}"
 fi
 
 for input in *.cpp; do
   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