AsmMatcher: emit subtarget feature enum in deterministic order.
TableGen: give asm match classes deterministic order.

TableGen was sorting the entries in some of its internal data
structures by pointer. This order filtered through to the final
matching table and affected the diagnostics produced on bad assembly
occasionally.

It also turns out STL algorithms are ridiculously easy to misuse on
containers with custom order methods. (No bugs before, or now that I
know of, but plenty in the middle).

This should fix the sanitizer bot, which ends up with weird pointers.