Try single quotes to fix the msys bot:

It was still failing with double quotes:

http://bb.pgr.jp/builders/clang-i686-msys/builds/698/steps/test_clang/logs/Clang%20%3A%3A%20Driver__cl.c

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187330 91177308-0d34-0410-b5e6-96231b3b80d8