[PATCH] Use the MS ABI for Win32 target by default

[Hans Wennborg]

  I'd really like to get this in, so trying to summarize where we are on the tests. I think these are the three tests that are still under discussion:

  test/CXX/class.access/p4.cpp
  The "Elide dtor access checks for pass-by-val objects in callees" patch at http://llvm-reviews.chandlerc.com/D2409 addresses this. Can we decide to make the expectations in this test depend on the outcome of that code review?

  test/SemaCXX/destructor.cpp
  The missing outermost level of template instantiation backtrace. I've commented on this.

  test/SemaCXX/virtual-base-used.cpp
  Adding "new D" to trigger vtable emission got pretty hairy here, so maybe we don't want to do that.

  Richard: I'm interested to hear your thoughts.

   - Hans

http://llvm-reviews.chandlerc.com/D2401