Fix EII

[AsakuraMizu]

Fix support for EII functions with defaults and EII statics. Now all tests/ui/eii tests pass.

[antoyo]

It seems there's some interactions with the inline attribute that should be handled as well.
For instance:

#![crate_type = "rlib"]
#![feature(extern_item_impls)]
#[eii(eii1)]
#[inline]
pub fn decl1(x: u64) {
    println!("default {x}");
}

panics with this warning:

libgccjit.so: warning: : inline function ‘_RNvCslJaV4vr0Uxj_9test_rust5decl1’ declared weak [-Wattributes]

Please add this as a test in tests/run and fix this issue.