Change all mips ports to use mips-unknown-openbsd2.0 like gcc does.

Change all mips ports to use mips-unknown-openbsd2.0 like gcc does.
This should allow for gdb to at least build on pmax, modulo potential platform
specific include files.    This impacts gas, ld, and other critical system
components.  Don't build this unless you are happy with your backups, as
always for a change of this nature.  It works for me on my machine, however.