Rust: export symbols may conflict

[peterhuene]

If we generate bindings for the following world foo:

package wit:repro

interface foo1 {
  foo: func()
}

interface foo2 {
  foo: func()
}

world foo {
  export foo1
  export foo2
}

The export_foo macro will generate the following conflicting decls:

// ...
macro_rules! export_foo(($t:ident) => {
  const _: () = {

    #[doc(hidden)]
    #[export_name = "wit:repro/foo1#foo"]
    #[allow(non_snake_case)]
    unsafe extern "C" fn __export_foo() {
      bindings::exports::wit::repro::foo1::call_foo::<$t>()
    }

    #[doc(hidden)]
    #[export_name = "wit:repro/foo2#foo"]
    #[allow(non_snake_case)]
    unsafe extern "C" fn __export_foo() {
      bindings::exports::wit::repro::foo2::call_foo::<$t>()
    }
  };

 // ...

The code that generates these decls uses just the method name.

The name should be based on the qualified name of the interface as well.

[alexcrichton]

Oh I thought these went in separate const: _: () = {...} blocks to not conflict, but that's apparently not the case. I think though we could wrap each individual function in such a block as well to avoid conflicts here to avoid having to invent a unique Rust name