[clang] [llvm] [WebAssembly] Represent reference types as TargetExtType (PR #203165)

[Hood Chatham via cfe-commits]

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hoodmane wrote:

Actually skipping this by returning false from selectCall does not work, it seems to result in `funcref.to_ptr` getting put by itself in a separate DAG which triggers the escape analysis. So I'll go back to using `dontUseFastISelFor()` to skip the whole block. 

https://github.com/llvm/llvm-project/pull/203165