COFF: Handle references from LTO object to lazy symbols correctly.

The code generator may create references to runtime library symbols such as
__chkstk which were not visible via LTOModule. Handle these cases by loading
the object file from the library, but abort if we end up having loaded any
bitcode objects.

Because loading the object file may have introduced new undefined references,
call reportRemainingUndefines again to detect and report them.

Differential Revision: http://reviews.llvm.org/D10332

llvm-svn: 239386