[WoA][MSVC] Use default linker setting in MSVC-compatible driver

At the moment "link.exe" is hard-coded as default linker in MSVC.cpp,
so there's no way to use LLD as default linker for MSVC driver.

This patch adds checking of CLANG_DEFAULT_LINKER to MSVC.cpp.

Reviewed By: asl

Differential Revision: https://reviews.llvm.org/D98493