Casting function pointers like this can break Emscripten [1]. In libxml2, I fixed all these issues 7 years ago. It can be painful, but "it worked for 28 years" is not an excuse.

[1] https://emscripten.org/docs/porting/guidelines/function_poin...

I believe AIX C++ name mangling includes function argument type information (with CV qualifiers!) so this is a real-world case where this does actually break. I suspect curl does not compile with the C++ compiler though.