Adds (most) support for ARC platform to port-independent mips code.
Some changes (e.g., clean up of overlapping CPU/FPU ids) inspired by
comparison to the OpenBSD 2.1 codebase of Soda's ARC port.
Open issues:
* Still no support for r4600 or mipsIV CPUs with two-way L1 cache.
Code derived from Per Fogelstrom's OpenBSD source doesn't work
on mips3 pmaxes with L2 cache.
* Still some port-specific #ifdefs, for interrupt enable and
pmax L2 cache-size. Needs more thought, but overlaps with
work-in-progress by Tohru and Tsubai on spl()s and related stuff.
Fixes profiling for non-underscore-prepending toolchains
(elf, e.g., shared libs), and breaks a.out/ecoff toolchains.
May break mips kernel profiling too. Needs more thought, since the
original intent of __mcount vs ___mcount on mips date back to pre-1.0 days.
consistent with the (default) prepending of underscores to identifiers.
Because this reference is inside an ASM string it's too hairy to
conditionalize to support different toolchains that don't prepend underscores.
(Just don't do profiling with such toolchains.)
