cmd/compile: loop inversion does not support unsigned numbers

[Jorropo]

This is duplicate of #61629 but for:

for range uint(x) {
 // ...
}

---

I didn't implemented it back then since I reused existing scanning code (findIndVar) which only supported signed ops:

go/src/cmd/compile/internal/ssa/loopbce.go

Line 99 in ef84d62

// TODO: Handle unsigned comparisons?

I'll submit a patch.

[gopherbot]

Change https://go.dev/cl/566437 mentions this issue: cmd/compile: add very basic unsigned matching to findIndVar