it calls make DLDFLAGS=$LDFLAGS which overrides $LDFLAGS completely. If $LDFLAGS contains some linking libraries, then the ebuild will emerge fine but not working. Some ebuilds have work-around by not calling gems_src_install.
The problem is that without that change, it tries to use the LDFLAGS used to build Ruby to build the rest (and they might not be adapt for that).
Perhaps we should patch mkmf :P I'll try to convice gem makers to use $libs instead of $LDFLAGS. Although I still want gems.eclass to append/override ldflags.
gems.eclass is no longer used for new packages. Closing WONTFIX.