MFC r312899: add octeon+ as an alias for octeon in GCC & binutils
r208737 added support for the "mips64r2" architecture and "octeon" CPU,
and the saa/saad instructions.
Upstream binutils also added the "octeon+" CPU, and the saa/saad
instructions are only available in octeon+, not octeon. Since our
base system tool chain already accepts saa/saad with -march=octeon,
just allow octeon+ as an alias.
This allows the use of octeon+ in kernel config files, for use with both
external tool chain and in-tree GCC/binutils.
Also includes GCC FBSD_CC_VER bump (r313041 in HEAD)
PR: 216516
Sponsored by: The FreeBSD Foundation