[clang] [lld] [llvm] [Wasm][Clang] Add support for pointer to externref (PR #163610)

[Sam Clegg via cfe-commits]

sbc100 wrote:

I think this is a continuation of the work that @pmatos started.  So CC'ing him in case he has any time to take a look.   Also @dschuff and @tlively 

Its quite a large and consequential change so perhaps you could describe here (or in the link a bug?) what you use case is and what kind of thing things unlock for you?

https://github.com/llvm/llvm-project/pull/163610