[llvm] [FuzzMutate] Match the callee's and callsite's calling conventions. (PR #139100)

[Manuel Carrasco via llvm-commits]

mgcarrasco wrote:

> @mgcarrasco Just curious what is your use case of FuzzMutate / IRFuzzer?

@DataCorrupted I'm currently working on fuzzing the AMDGPU backend. Thanks for your reviews.

https://github.com/llvm/llvm-project/pull/139100