[llvm] Make `IntrinsicLowering` external function call lowering configurable (PR #102148)

[Matt Arsenault via llvm-commits]

arsenm wrote:

This whole area is a mess with redundant handling. I think this pass needs to be broken down into a set of utility functions, and not turned into a point of configuration. I think this version is only used by fast-isel, and ignores any kind of legality checks.

https://github.com/llvm/llvm-project/pull/102148