[llvm] [DWARF] Emit line 0 source locations for BB padding nops (PR #99496)

[Orlando Cazalet-Hyams via llvm-commits]

OCHyams wrote:

cc @dwblaikie, for some context, we noticed this as it manifested in our debugger "step-over"-ing to an out of scope line number (a loop alignment nop inherited the source location from an inlined instruction before it). GDB and LLDB seem to avoid running into that issue while stepping over but it can still be observed while stepping at an instruction level. Either way, a code alignment nop feels unambiguously like an instruction that should be line-zeroed to me. wdyt?

https://github.com/llvm/llvm-project/pull/99496