Interpreter doesn't wrap extern fun vars in Crystal procs

[asterite]

This code crashes the interpreter:

x = LibPCRE.free
x.call(Pointer(Void).new(0))

The problem is that LibCPRE.free's type is Proc(Void*). Right now Crystal returns that type from LibPCRE.free, which is 16 bytes, but that's wrong. The actual size is 8 bytes and it needs to be wrapped in a FFI closure and then padded with zero to form the Proc.

[straight-shoota]

For reference: This was discovered in #12456 (comment)

[asterite]

Also a note that I briefly thought how to implement this but I have no idea. I get confused. And I won't have time to do this. So if someone wants to do it, please go ahead :-)

I also noticed that things like ->foo doesn't work either in the interpreter.

[HertzDevil]

This is also related to the Proc.new(Void*, Void*) constructor in case the C function returns a type-erased pointer, since that can directly implement the use case here. Crystal::System::Socket.load_extension_function on Windows does this and it is currently blocking any form of networking in interpreted code on Windows.

We should decide whether that constructor accepts bytecode pointers or C function pointers.