Use `ld -f' (actually `cc -Wl,-f') at `make depend' time to generate

Use `ld -f' (actually `cc -Wl,-f') at `make depend' time to generate
almost perfect dependencies on crt0's and libraries.  DPADD and
bsd.libnames.mk should go away soon.  Use a new _EXTRADEPEND target
to implement this and to avoid editing of .depend when .depend isn;t
being rebuilt.  The afterdepend target doesn't seem to be good for
anything and is now unused.

Fixed LDDESTDIR for the DESTDIR case when ${SHLIBDIR} != /usr/lib.

Added commented-out -nostdlib to LDDESTDIR for the DESTDIR case.
The wrong libraries may be used without this; however it breaks
linkage to crt0 and libc.