[clang] [flang] [llvm] [mlir] [DebugInfo][RemoveDIs] Rip out the UseNewDbgInfoFormat flag (PR #143207)

[Jeremy Morse via llvm-commits]

jmorse wrote:

Removing the `--experimental-debuginfo-iterators` flag from 1 flang and 1 mlir test too -- the flag has been a dummy for a month and doesn't do anything, the extra RUNlines were just extra coverage for when intrinsic support was still feasible.

https://github.com/llvm/llvm-project/pull/143207