Don't drop types with no drop glue when building drops for tailcalls

[WaffleLapkin]

this is required as otherwise drops of &mut refs count as a usage of a
'two-phase temporary' causing an ICE.

fixes #128097

The underlying issue is that the current code generates drops for &mut which are later counted as a second use of a two-phase temporary:

bat t.rs -p

#![expect(incomplete_features)]
#![feature(explicit_tail_calls)]

fn f(x: &mut ()) {
    let _y = String::new();
    become f(x);
}

fn main() {}

rustc t.rs -Zdump_mir=f

error: internal compiler error: compiler/rustc_borrowck/src/borrow_set.rs:298:17: found two uses for 2-phase borrow temporary _4: bb2[1] and bb3[0]
 --> t.rs:6:5
  |
6 |     become f(x);
  |     ^^^^^^^^^^^


thread 'rustc' panicked at compiler/rustc_borrowck/src/borrow_set.rs:298:17:
Box<dyn Any>
stack backtrace:
[REDACTED]

error: aborting due to 1 previous error

bat ./mir_dump/t.f.-------.renumber.0.mir -p -lrust

// MIR for `f` 0 renumber

fn f(_1: &mut ()) -> () {
    debug x => _1;
    let mut _0: ();
    let mut _2: !;
    let _3: std::string::String;
    let mut _4: &mut ();
    scope 1 {
        debug _y => _3;
    }

    bb0: {
        StorageLive(_3);
        _3 = String::new() -> [return: bb1, unwind: bb4];
    }

    bb1: {
        FakeRead(ForLet(None), _3);
        StorageLive(_4);
        _4 = &mut (*_1);
        drop(_3) -> [return: bb2, unwind: bb3];
    }

    bb2: {
        StorageDead(_3);
        tailcall f(Spanned { node: move _4, span: t.rs:6:14: 6:15 (#0) });
    }

    bb3 (cleanup): {
        drop(_4) -> [return: bb4, unwind terminate(cleanup)];
    }

    bb4 (cleanup): {
        resume;
    }
}

Note how _4 is moved into the tail call in bb2and dropped inbb3`.

This PR adds a check that the locals we drop need dropping.

r? @oli-obk (feel free to reassign, I'm not sure who would be a good reviewer, but thought you might have an idea)
cc @beepster4096, since you wrote the original drop implementation.

[oli-obk]

r=me with crash test removed and comment updated

[rustbot]

The Miri subtree was changed

cc @rust-lang/miri

[WaffleLapkin]

@bors r=@oli-obk

[bors]

📌 Commit 9b82f20 has been approved by oli-obk

It is now in the queue for this repository.