lang/perl5*: alternative workaround for lld 15 and dtrace enabled

Modify the workaround committed in 4ae8ff941b29 by only adding
-Wl,--allow-multiple-definition to the two link command lines that
require it, instead of adding it to hints/freebsd.sh

Otherwise, that linker flag is emitted into perl's global configuration
(/usr/local/lib/perl5/5.xx/mach/Config_heavy.pl), and might be used by
other ports which link in libperl, such as www/mod_perl2, which cannot
correctly handle any unexpected linker flags, leading to errors.

PR: 265516
Reported by: lev
Approved by: maintainer timeout (1 month)
Fixes: 4ae8ff941b29
MFH: 2022Q3