Remove further unwanted linker flags from perl_embed_ldflags

Remove further unwanted linker flags from perl_embed_ldflags

Remove the contents of $Config{ldflags} from ExtUtils::Embed's ldopts,
like we already do with $Config{ccdlflags}.  Those flags are the
choices of those who built the Perl installation, which are not
necessarily appropriate for building PostgreSQL.  What we really want
from ldopts are the options identifying the location and name of the
libperl library, but unfortunately it doesn't appear possible to get
that separately from the other stuff.

The motivation for this was to strip -mmacosx-version-min options.  We
already did something similar for the -arch option.  Both of those are
now covered by this more general approach.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://www.postgresql.org/message-id/flat/8c4fcb72-2574-ff7c-4c25-1f032d4a2a57%40enterprisedb.com