arch/Toolchain.defs: Change all ARCROSSDEV to CROSSDEV

[xiaoxiang781216]

Summary

ARCROSSDEV always equals to CROSSDEV, so it is no reason to keep ARCROSSDEV.

Impact

No visible change.

Testing

[btashton]

Why not just define ARCROSSDEV for the three architectures that are missing it? If we do remove it, than we should also remove the definitions of it.

It is missing from from mips32 avr32 avr mor1kx

[xiaoxiang781216]

Why not just define ARCROSSDEV for the three architectures that are missing it? If we do remove it, than we should also remove the definitions of it.

It is missing from from mips32 avr32 avr mor1kx

I remove ARCROSSDEV because it is always same as CROSSDEV, which could also simplify user setup, but I can add ARCROSSDEV for mips32 avr32 avr mor1kx if you prefer.

[btashton]

I did not see where you removed the ARCROSSDEV for arm in the diff UI, but I see it now. Sorry for the confusion.
I think this is probably safe, I cannot think of a good reason for using a different binutils than the one that would have come with the rest of the cross toolchain.