Eliminate ptr->int->ptr casting from Identifier implementation

[dtolnay]

This lets us pass Miri's raw pointer tagging.

[saethlin]

This is much sleeker. I like it.

By eye it looks like this could accommodate a target where pointers are 16 bytes. I don't think the flexibility gets in the way, but is there a way to test that this works on such a target?

[dtolnay]

Yeah this doesn't particularly care how big a pointer is. 16 bit, 32 bit, 64 bit, 128 bit should all work.

It's possible Miri could add some made-up target specifications for testing such scenarios. Changes to libcore might also be required though.