restrictions for mips hosts. * config/mips/{xm-irix3.h, xm-mips.h, xm-news-mips.h, xm-riscos.h}: Use it.
rather than including xm-bigmips.h.
config files moved to an appropriate config/<cpu> subdirectory. * nm-*, xm-*, tm-*: All native, host, and target files, which get linked to nm.h, xm.h, and tm.h respectively by configure, moved to appropriate config/<cpu> subdirectory.