[DebugInfo] Soft-disable the production of debug intrinsics (#133933)
This patch switches the --experimental-debuginfo-iterators flag to be
stored to an otherwise unused cl-opt. This is a deliberate attempt to
break downstream tests that are relying on the use of debug intrinsics,
because they're imminently going away! If this commit breaks your tests,
please just revert the commit upstream, and then make contact with us
here:
https://discourse.llvm.org/t/psa-ir-output-changing-from-debug-intrinsics-to-debug-records/79578
So that we can work out whether there's any further transition work
needed to support the move away from using debug intrinsics.