Continuing work from #18344, be more conservative about when we load
SwiftOnoneSupport. Specifically, -emit-silgen and -emit-sibgen, despite
not going through the SIL Optimizer, may silently introduce dependencies
on SwiftOnoneSupport.
Because we want to support the ability to posthumously compile SILGen
and SIBGen'd files with these implicit dependencies, and because SIL
is not yet capable of expressing the dependency itself, we must always
assume we need to load SwiftOnoneSupport.
