Fix Altivec vector literal parser hack for C++11.

It doesn't make any sense to accept "..." in the argument to a C-style cast,
so use a separate expression list parsing routine which rejects it. PR16874.
clang-cl: Support /link option and set target to win32

This adds support for the /link option, which forwards
subsequent arguments to the linker.

The test for this will only work when targetting win32.
Since that's the only target where clang-cl makes sense,
use that target by default.

Differential Revision: http://llvm-reviews.chandlerc.com/D1388