Update from https://crrev.com/327068

tools/clang/plugins/tests/test.sh

Index: tools/clang/plugins/tests/test.sh
diff --git a/tools/clang/plugins/tests/test.sh b/tools/clang/plugins/tests/test.sh
index ea2105446f07ace607cbed8c587b2c476ac934ca..cf262522eb855e291b8f769638bcddce0e9f7114 100755
--- a/tools/clang/plugins/tests/test.sh
+++ b/tools/clang/plugins/tests/test.sh
@@ -12,6 +12,8 @@ E_FAILEDTEST=1
 
 failed_any_test=
 
+THIS_DIR="$(dirname "${0}")"
+
 # Prints usage information.
 usage() {
   echo "Usage: $(basename "${0}")" \
@@ -38,6 +40,7 @@ do_testcase() {
 
   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}")"
@@ -81,7 +84,7 @@ else
 
   # 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