Implement TokenizeWindowsCommandLine.

This is a follow up patch for r187390 to implement the parser for the
Windows-style command line. This should follow the rule as described
at http://msdn.microsoft.com/en-us/library/windows/desktop/17w5ykft(v=vs.85).aspx

Differential Revision: http://llvm-reviews.chandlerc.com/D1235