Add unwind information to mips epilogues

[Richard Sandiford]

Richard Sandiford <rdsandiford@googlemail.com> writes:
> Gah, my bad, sorry.  I'd forgotten mipsisa32-elf is EABI32
> rather than o32.  mips-elf with -mips32/-mips16 would test
> what I was after.

Sigh.  Obviously not my day.  I just remembered that the default
mips-elf simulator won't accept -mips32 instructions, so you need
to play some tricks.  Could you just try some of the spot checks
instead?  I'll test GNU/Linux on qemu once everything is in.

Richard