If LLVM optimizations are to be disabled, we cannot just not run all LLVM passes, because there are some mandatory LLVM passes, like coro splitting.
Instead, just run the -O0 LLVM pipeline if -disable-llvm-optzns is used.
Fixes compiler crashes if -disable-llvm-optzns is used.
Note: if one wants to see the output of IRGen, -emit-irgen can be used.
Do not gate the coroutine extension points on the LLVM passes. Without
running this pass, the generated IR cannot be used by the LLVM tooling.
This allows generating the LLVM IR to debug issues in the LLVM backend.
I encountered this when trying to isolate a debug info generation bug
which seems to be caused by the SRoA pass in LLVM. By allowing to emit
the LLVM IR without the LLVM optimizations, it is possible to isolate
the LLVM pass operation via `opt` from LLVM.
