Everything that comes after -- should be treated as a filename. This
enables passing in filenames that would otherwise be conflated with
command-line options.
This is especially important for clang-cl which supports options
starting with /, which are easily conflatable with Unix-style
path names.
Differential Revision: http://llvm-reviews.chandlerc.com/D1274
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187675
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