test/Driver/cl.c, remove quotes around /help

The quotes (from r187330) didn't really help here, the trick was to disable
the test on MSYS builds. This removes those quotes, changes back the comment
to explain why /? has to be quoted specifically, and moves the REQUIRES
line to the top of the file because that's important.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187366 91177308-0d34-0410-b5e6-96231b3b80d8