clang-cl: Support the run-time selection options (/MD, /MT et al.)

These flags set some preprocessor macros and injects a dependency
on the runtime library into the object file, which later is picked up
by the linker.

This also adds a new CC1 flag for adding a dependent library.

Differential Revision: http://llvm-reviews.chandlerc.com/D1315

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@187945 91177308-0d34-0410-b5e6-96231b3b80d8