[llvm] [WebAssembly] Fix signatures of frexpf family of libcalls (PR #133289)

[Sam Clegg via llvm-commits]

sbc100 wrote:

> LGTM too but if you want to improve the tests, they are in [llvm/test/CodeGen/WebAssembly/libcalls.ll](https://github.com/llvm/llvm-project/blob/main/llvm/test/CodeGen/WebAssembly/libcalls.ll). It looks like it covers frexp but It actually doesn't look like we have coverage for memory64 at all.

I looked into modifying `test/CodeGen/WebAssembly/libcalls.ll` and using `-DPTR=i32/i64` to make it pass in both modes.  But then I realized that its output is auto-generated/auto-updated.  So that other option is it clone that test and make a separate file, but that makes it little harder to see how the wasm32 and wasm64 version vary.

What is the best approach here?  Clone it and use auto-updated?  Or stop using auto-update and manually encode the differences?

I'm think a clone will be easier in the long run, even though it involves some duplication.

@tlively @dschuff WDYT?

https://github.com/llvm/llvm-project/pull/133289