entirely get rid of NeedsRfc CTFE errors

compiler/rustc_const_eval/src/const_eval/error.rs

@@ -15,7 +15,6 @@ use crate::interpret::{
 /// The CTFE machine has some custom error kinds.
 #[derive(Clone, Debug)]
 pub enum ConstEvalErrKind {
-    NeedsRfc(String),
     ConstAccessesStatic,
     ModifiedGlobal,
     AssertFailure(AssertKind<ConstInt>),
@@ -42,9 +41,6 @@ impl fmt::Display for ConstEvalErrKind {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         use self::ConstEvalErrKind::*;
         match *self {
-            NeedsRfc(ref msg) => {
-                write!(f, "\"{}\" needs an rfc before being allowed inside constants", msg)
-            }
             ConstAccessesStatic => write!(f, "constant accesses static"),
             ModifiedGlobal => {
                 write!(f, "modifying a static's initial value from another static's initializer")

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -340,11 +340,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
 
         // CTFE-specific intrinsics.
         let Some(ret) = target else {
-            return Err(ConstEvalErrKind::NeedsRfc(format!(
+            throw_unsup_format!("intrinsic `{intrinsic_name}` is not supported at compile-time");
-                "calling intrinsic `{}`",
-                intrinsic_name
-            ))
-            .into());
         };
         match intrinsic_name {
             sym::ptr_guaranteed_eq | sym::ptr_guaranteed_ne => {
@@ -401,11 +397,9 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
                 }
             }
             _ => {
-                return Err(ConstEvalErrKind::NeedsRfc(format!(
+                throw_unsup_format!(
-                    "calling intrinsic `{}`",
+                    "intrinsic `{intrinsic_name}` is not supported at compile-time"
-                    intrinsic_name
+                );
-                ))
-                .into());
             }
         }
 
@@ -448,7 +442,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         _left: &ImmTy<'tcx>,
         _right: &ImmTy<'tcx>,
     ) -> InterpResult<'tcx, (Scalar, bool, Ty<'tcx>)> {
-        Err(ConstEvalErrKind::NeedsRfc("pointer arithmetic or comparison".to_string()).into())
+        throw_unsup_format!("pointer arithmetic or comparison is not supported at compile-time");
     }
 
     fn before_terminator(ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {

src/test/ui/consts/miri_unleashed/ptr_arith.rs

@@ -19,4 +19,7 @@ static PTR_INT_TRANSMUTE: () = unsafe {
     //~| unable to turn pointer into raw bytes
 };
 
+// I'd love to test pointer comparison, but that is not possible since
+// their `PartialEq` impl is non-`const`.
+
 fn main() {}