Merging r143801:

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r143801 | chandlerc | 2011-11-05 02:24:44 -0700 (Sat, 05 Nov 2011) | 20 lines

Fix a significant oversight in my move of MSVC includes to the driver:
actually manage the builtin header file includes as well as the system
ones.

This one is actually debatable whether it belongs in the driver or not,
as the builtin includes are really an internal bit of implementation
goop for Clang. However, they must be included at *exactly* the right
point in the sequence of header files, which makes it essentially
impossible to have this be managed by the Frontend and the rest by the
Driver. I have terrible ideas that would "work", but I think they're
worse than putting this in the driver and making the Frontend library
even more ignorant of the environment and system on which it is being
run.

Also fix the fact that we weren't properly respecting the flags which
suppress standard system include directories.

Note that this still leaves all of the Clang tests which run CC1
directly and include builtin header files broken on Windows. I'm working
on a followup patch to address that.
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llvm-svn: 143932