Fix Windows bot failures from r268627

Remove "/" path separator from expected pattern which should fix a
couple of Windows bots that have failed:

http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-scei-ps4-windows10pro-fast/builds/4816
http://bb.pgr.jp/builders/ninja-clang-i686-msc19-R/builds/2610

llvm-svn: 268629