[clang-cl] Use the Windows response file tokenizer

We were still using the Unix response file tokenizer for all driver
modes. This was difficult to get right in the beginning because there is
a circular dependency. The Driver class also can't officially determine
its mode until it can see all possible --driver-mode= flags, and those
flags could come from the response file.

Now we use the Windows parsing algorithm if the program name looks like
clang-cl, or if the --driver-mode=cl flag is present on the main command
line.

Fixes PR23709.

Reviewers: hans

Differential Revision: http://reviews.llvm.org/D11229

llvm-svn: 242346