env MACOSX_DEPLOYMENT_TARGET=10.3 cc -o libperl.5.10.1.dylib -dynamiclib -compatibility_version 5.10.0 -current_version 5.10.1 -install_name /Library/Gentoo/usr/lib/perl5/5.10.1/powerpc-darwi/CORE/libperl.5.10.dylib op.o perl.o gv.o toke.o perly.o pad.o regcomp.o dump.o util.o mg.o reentr.o mro.o hv.o av.o run.o pp_hot.o sv.o pp.o scope.o pp_ctl.o pp_sys.o doop.o doio.o regexec.o utf8.o taint.o deb.o universal.o xsutils.o globals.o perlio.o perlapi.o numeric.o mathoms.o locale.o pp_pack.o pp_sort.o DynaLoader.o -ldl -lm -lc -Wl,-soname -Wl,libperl.so.`echo libperl.5.10.1.dylib | cut -d. -f3,4` ld: unknown option: -soname as you can see, the perl buildsystem already has something in place to set the soname (install_name on Darwin), hence consider the attached patch which is more portable and doesn't break builds on various Prefix arches
Created attachment 205531 [details, diff] perl-5.10.1-prefix-soname.patch
patch added to -7. Thanks