Auto merge of #139309 - RalfJung:abi_unsupported_vector_types, r=fee1-dead,traviscross

make abi_unsupported_vector_types a hard error

Fixes rust-lang/rust#116558 by completing the transition; see that issue for context. The lint was introduced with Rust 1.84 and this has been shown in cargo's future breakage reports since Rust 1.85, released 6 weeks ago, and so far we got 0 complaints by users. There's not even a backlink on the tracking issue. We did a [crater run](rust-lang/rust#127731 (comment)) when the lint was originally added and found no breakage. So I don't think we need another crater run now, but I can do one if the team prefers that.

rust-lang/rust#131800 is done, so for most current targets (in particular, all tier 1 and tier 2 targets) we have the information to implement this check (modulo the targets where we don't properly support SIMD vectors yet, see the sub-issues of rust-lang/rust#116558). If a new target gets added in the future, it will default to reject all SIMD vector types until proper information is added, which is the default we want.

This will need approval by for `@rust-lang/lang.` Cc `@workingjubilee` `@veluca93`

try-job: test-various
try-job: armhf-gnu
try-job: dist-i586-gnu-i586-i686-musl

Author: bors

example/std_example.rs

@@ -8,9 +8,6 @@
     unboxed_closures
 )]
 #![allow(internal_features)]
-// FIXME once abi_unsupported_vector_types is a hard error disable the foo test when the respective
-// target feature is not enabled.
-#![allow(abi_unsupported_vector_types)]
 
 #[cfg(target_arch = "x86_64")]
 use std::arch::x86_64::*;