[LLD] [MinGW] Look for other library patterns with -l

GNU ld looks for a number of other patterns than just lib<name>.dll.a
and lib<name>.a.

GNU ld does support linking directly against a DLL without using an
import library. If that's the only match for a -l argument, point out
that the user needs to use an import library, instead of leaving the
user with a puzzling message about the -l argument not being found
at all.

Also convert an existing case of fatal() into error().

Differential Revision: https://reviews.llvm.org/D68689

llvm-svn: 374292