stage2: implement `@clz` and `@ctz`

Also improve the LLVM backend to support lowering bigints to LLVM
values.

Moves over a bunch of math.zig test cases to the "passing for stage2"
section.
33e77f127dAndrew Kelley committed on 9/29/2021, 5:38:51 AMparent7efc2a0
12 files changedLine totals unavailable