Auto merge of #95149 - cjgillot:once-diag, r=estebank

Remove `Session::one_time_diagnostic`

This is untracked mutable state, which modified the behaviour of queries.
It was used for 2 things: some full-blown errors, but mostly for lint declaration notes ("the lint level is defined here" notes).

It is replaced by the diagnostic deduplication infra which already exists in the diagnostic emitter.
A new diagnostic level `OnceNote` is introduced specifically for lint notes, to deduplicate subdiagnostics.

As a drive-by, diagnostic emission takes a `&mut` to allow dropping the `SubDiagnostic`s.

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/rustc_codegen_ssa/src/back/write.rs b/compiler/rustc_codegen_ssa/src/back/write.rs
index e23572104c4..1d11e6dfbd2 100644
--- a/compiler/rustc_codegen_ssa/src/back/write.rs
+++ b/compiler/rustc_codegen_ssa/src/back/write.rs
@@ -1748,7 +1748,7 @@ impl SharedEmitterMain {
                     if let Some(code) = diag.code {
                         d.code(code);
                     }
-                    handler.emit_diagnostic(&d);
+                    handler.emit_diagnostic(&mut d);
                 }
                 Ok(SharedEmitterMessage::InlineAsmError(cookie, msg, level, source)) => {
                     let msg = msg.strip_prefix("error: ").unwrap_or(&msg);