[LLD] [MinGW] Print errors/warnings in lld-link with a "ld.lld" prefix

Pass the original argv[0] to the coff linker, as the coff linker uses
the basename of argv[0] as the log prefix.

This makes error messages to be printed with a "ld.lld:" prefix
instead of "lld-link:". The current "lld-link:" prefix can be confusing
to users, as they're invoking the MinGW linker (and might not even have
a lld-link executable).

Keep the first argument as lld-link when printing the command line, to
make it an actually reproducible standalone command.

Differential Revision: https://reviews.llvm.org/D104526