intrinsics: use const generic to set atomic ordering

compiler/rustc_codegen_ssa/src/errors.rs

@@ -796,22 +796,6 @@ pub(crate) struct ShuffleIndicesEvaluation {
     pub span: Span,
 }
 
-#[derive(Diagnostic)]
-#[diag(codegen_ssa_missing_memory_ordering)]
-pub(crate) struct MissingMemoryOrdering;
-
-#[derive(Diagnostic)]
-#[diag(codegen_ssa_unknown_atomic_ordering)]
-pub(crate) struct UnknownAtomicOrdering;
-
-#[derive(Diagnostic)]
-#[diag(codegen_ssa_atomic_compare_exchange)]
-pub(crate) struct AtomicCompareExchange;
-
-#[derive(Diagnostic)]
-#[diag(codegen_ssa_unknown_atomic_operation)]
-pub(crate) struct UnknownAtomicOperation;
-
 #[derive(Diagnostic)]
 pub enum InvalidMonomorphization<'tcx> {
     #[diag(codegen_ssa_invalid_monomorphization_basic_integer_type, code = E0511)]