tests/debuginfo/macro-stepping.rs remains broken with SingleUseConsts

[khuey]

This is the part of @saethlin's #128945 that survived #130329. Reordering the IR in the front end in the SingleUseConsts pass breaks the stepping order. This could be mitigated to some extent (but not completely, unclear if it would be sufficient for this test to pass) with better support in LLVM for front ends to express which IR instructions should be considered for breakpoints.

@rustbot label +A-debuginfo +A-testsuite +A-llvm +A-mir +C-bug +T-compiler +WG-debugging +WG-llvm