Teach the include sorting script about the gtest headers; sort them with

the system headers.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169242 91177308-0d34-0410-b5e6-96231b3b80d8

utils/sort_includes.py

@@ -35,7 +35,7 @@ def sort_includes(f):
         api_headers.append(header)
         look_for_api_header = False
         continue
-      if header.startswith('<'):
+      if header.startswith('<') or header.startswith('"gtest/'):
         system_headers.append(header)
         continue
       if (header.startswith('"llvm/') or header.startswith('"llvm-c/') or