[ORC][ORC_RT][COFF] Support dynamic VC runtime.

Supports dynamic VC runtime. It implements atexits handling which is required to load msvcrt.lib successfully. (the object file containing atexit symbol somehow resolves to static vc runtim symbols) It also default to dynamic vc runtime which tends to be more robust.

Reviewed By: lhames

Differential Revision: https://reviews.llvm.org/D132525