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

[Derek Schuff via llvm-commits]

dschuff 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.

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