[AlwaysInline] Avoid unnecessary BFI fetches (#117750)

AlwaysInliner doesn't use BFI itself, it only updates it. If BFI is not
already computed, it will spend time to first compute it, and then
update it. This is not necessary: If BFI is not available in the first
place, there is no need to update it.

This is mainly relevant in debug builds for IR that has a lot of
alwaysinline functions.