mips fast-isel port

Not that I think there is much chance that anyone else is thinking of submitting fast-isel patches for Mips but...

I am very far a long in this port; almost to where the ARM port for example was when they first enabled fast-isel as the default for -O0.
It's not really our plan to make this the default right now but I'm just saying where we are.

I'm starting to catch up on the patch push and review so hopefully I will get it all in over the next few weeks.

Just a warning to anyone wanting to add to what is there that it would for sure conflict with what is in my
plan.

I have reorganized it all now to be as close as possible to the AARch64 fast-isel port which seems to be the
cleanest to me and especially in call lowering and call return and some of the other more complex areas.
This reorganization is a later one in my queue of patches but that is where it is all at right now internally at Mips.

I'm so close to AARch64 port that I think that seriously in the future this could all be merged into target independent
code with some small amount of virtual functions or other configuration methods.

All the hard things have been implemented so my belief is that the rest will go quickly with the AArch64 as the main
reference design; of course consulting the other ports too.

Reed

Not a bad idea, however, why aren't you doing this incrementally?

-eric