[llvm] [CodeGen][ISel] Fix inline assembly crash during instruction selection with direct memory output constraint (PR #209439)

[Chibuoyim Ogbonna via llvm-commits]

bruteforceboy wrote:

> I think there might be a similar pre-existing bug with `=p` not being rejected as output constraint, resulting in an assert. Might be worth checking on that since the fix would likely have a similar shape?
> 
> https://godbolt.org/z/4h8r4E93f

I've now rejected this as an output constraint and added tests.

https://github.com/llvm/llvm-project/pull/209439