The main branch does not compile any more in CI

[stephanemagnenat]

Describe the Bug

The main branch does not compile any more in CI because of a deprecation warning Clippy Lint.

@alexcrichton / @daxpedda I ping you because I do not know anyone else, who is the current active maintainer to ping for such issues?

Steps to Reproduce

See my blank PR (#4481)

Expected Behavior

I expect main to compile.

Actual Behavior

See:

error: extern declarations without an explicit ABI are deprecated
   --> src/closure.rs:602:24
    |
602 |                   unsafe extern fn destroy<$($var: FromWasmAbi,)* R: ReturnWasmAbi>(
    |                          ^^^^^^ help: explicitly specify the "C" ABI: `extern "C"`
...
749 | / doit! {
750 | |     ()
751 | |     (A a1 a2 a3 a4)
752 | |     (A a1 a2 a3 a4 B b1 b2 b3 b4)
...   |
758 | |     (A a1 a2 a3 a4 B b1 b2 b3 b4 C c1 c2 c3 c4 D d1 d2 d3 d4 E e1 e2 e3 e4 F f1 f2 f3 f4 G g1 g2 g3 g4 H h1 h2 h3 h4)
759 | | }
    | |_- in this macro invocation
    |
    = note: `-D missing-abi` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(missing_abi)]`
    = note: this error originates in the macro `doit` (in Nightly builds, run with -Z macro-backtrace for more info)