[llvm] [DebugInfo] Add num_extra_inhabitants to debug info (PR #112590)

[David Blaikie via llvm-commits]

dwblaikie wrote:

Can you include some of these details in the description/commit message? 
(this bit, or something like it, especially: "Since Swift generics are not monomorphized, by using dynamic libraries you can have generic types whose size, alignment, etc, are known only at runtime (which is why this feature is needed).")

https://github.com/llvm/llvm-project/pull/112590