[Support] Fix argv string escape bug on Windows
Summary:
This is http://llvm.org/PR15802. Backslashes preceding double quotes in
arguments must be escaped. The interesting bit is that all other
backslashes should *not* be escaped, because the un-escaping logic is
only triggered by the presence of a double quote character.
Reviewers: Bigcheese
CC: llvm-commits
Differential Revision: http://llvm-reviews.chandlerc.com/D705
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180035
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