arch/mips: Set emul list (EMULATIONS) and default emul (DEFAULT_EMULATION) in Makefile.inc. Add mips-elf emul vector to SRCS. config.h: add #ifndef/#endif srapper around overridden tokens.
(It's too hard, perhaps impossible, to set them correctly in config.h.) #error out if they're not defined.
'dist' tree for NetBSD/arm32. Other ports can follow as support is added for each port.