Handle consecutive-double-quotes in Windows argument parsing

Windows command line argument processing treats consecutive double quotes
as a single double-quote. This patch implements this functionality.

Differential Revision: https://reviews.llvm.org/D58662



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@356193 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed