[COFF][LLD] Add link support for Microsoft precompiled headers OBJs

This change allows for link-time merging of debugging information from
Microsoft precompiled types OBJs compiled with cl.exe /Z7 /Yc and /Yu.

This fixes llvm.org/PR34278

Differential Revision: https://reviews.llvm.org/D45213

llvm-svn: 346154