print/openprinting: fix build when lld is the system linker

This port passes an invalid argument -Mmapfile to the linker. Per GNU
BFD ld's manpage, link map options are -M or --print-map to print a link
map to stdout, or -Map mapfile to print a link map to mapfile.

It appears that ld.bfd accepts -Mmapfile as a synonym for -M due to some
quirk of its parser; lld simply fails with an unknown argument error.

This port's embedded copy of libtool was also too old to know that it
should pass the -fuse-ld flag from LDFLAGS through to the linker, and
also too old to match the sed expression in Mk/Uses/libtool.mk that
patches in knowledge of -fuse-ld. Thus, patch ltmain.sh to add
-fuse-ld=bfd as a passthrough flag.

I do not know why libtool's authors believed that silently dropping
flags from a user's provided LDFLAGS was (is) a sensible thing to do.

PR: 221809
Approved by: ler
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D14968