Tweaks to make libraries and make installworld

• Optimize/fix _prereq_libs and _generic_libs by not installing the .gcno files with "make install". This cuts down on installing unnecessary files to WORLDTMP and fixes the build, since BSD.coverage.dist wasn't being splatted on WORLDTMP.
• Splat BSD.coverage.dist on ${DESTDIR}/usr/lib in distributeworld/installworld so the files will be installed to the proper places.