Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Make sure legacy stuff comes last. Some tools that use
legacy stuff (binutils) depend on this order.

For this to work, provide (and use) specialized versions
of bsd.prog.mk and bsd.lib.mk that include the standard
versions first, then augment CFLAGS, DPADD, LDADD, and
LDFLAGS as necessary, with the legacy stuff.

Tested on: 4.0-RELEASE