Auto merge of #141435 - RalfJung:unsupported_calling_conventions, r=workingjubilee

Add (back) `unsupported_calling_conventions` lint to reject more invalid calling conventions

This adds back the `unsupported_calling_conventions` lint that was removed in https://github.com/rust-lang/rust/pull/129935, in order to start the process of dealing with https://github.com/rust-lang/rust/issues/137018. Specifically, we are going for the plan laid out [here](https://github.com/rust-lang/rust/issues/137018#issuecomment-2672118326):
- thiscall, stdcall, fastcall, cdecl should only be accepted on x86-32
- vectorcall should only be accepted on x86-32 and x86-64

The difference to the status quo is that:
- We stop accepting stdcall, fastcall on targets that are windows && non-x86-32 (we already don't accept these on targets that are non-windows && non-x86-32)
- We stop accepting cdecl on targets that are non-x86-32
- (There is no difference for thiscall, this was already a hard error on non-x86-32)
- We stop accepting vectorcall on targets that are windows && non-x86-*

Vectorcall is an unstable ABI so we can just make this a hard error immediately. The others are stable, so we emit the `unsupported_calling_conventions` forward-compat lint. I set up the lint to show up in dependencies via cargo's future-compat report immediately, but we could also make it show up just for the local crate first if that is preferred.

try-job: i686-msvc-1
try-job: x86_64-msvc-1
try-job: test-various

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/rustc_target/src/spec/mod.rs b/compiler/rustc_target/src/spec/mod.rs
index 1726de4d471..6ceb5e80f21 100644
--- a/compiler/rustc_target/src/spec/mod.rs
+++ b/compiler/rustc_target/src/spec/mod.rs
@@ -62,7 +62,7 @@ mod abi_map;
 mod base;
 mod json;
 
-pub use abi_map::AbiMap;
+pub use abi_map::{AbiMap, AbiMapping};
 pub use base::apple;
 pub use base::avr::ef_avr_arch;