Use BUILDSYMLINKS instead of home-grown equivalents.
added if $DESTDIR is set by the bsd.dep.mk and bsd.prog.mk magic, but caused problems while not using build.sh.
- regenerate for most platforms. missing: m68000, alpha, sh3eb.
- clean up commented & wrong rules - find the right bits/ headers for sparc64 & arm - make sure libsupc++/libstdc++ have all the symbols from libiberty they want - disable the build of libstdc++ for now (but keep the includes installing)
