zir: add negate/negate_wrap, implement astgen

These were previously implemented as a sub/sub_wrap instruction with a
lhs of 0. Making this separate instructions however allows us to save
some memory as there is no need to store a lhs.
310a44d5beIsaac Freund committed on 3/21/2021, 7:32:39 PMparent7800ae0
4 files changedLine totals unavailable