Rollup merge of #89508 - jhpratt:stabilize-const_panic, r=joshtriplett

Stabilize `const_panic`

Closes #51999

FCP completed in #89006

```@rustbot``` label +A-const-eval +A-const-fn +T-lang

cc ```@oli-obk``` for review (not `r?`'ing as not on lang team)

1 files changed, 6 insertions, 2 deletions

diff --git a/compiler/rustc_index/src/vec.rs b/compiler/rustc_index/src/vec.rs
index 56ea04539e5..88315246834 100644
--- a/compiler/rustc_index/src/vec.rs
+++ b/compiler/rustc_index/src/vec.rs
@@ -124,7 +124,9 @@ macro_rules! newtype_index {
 
             #[inline]
             $v const fn from_usize(value: usize) -> Self {
-                // FIXME: replace with `assert!(value <= ($max as usize));` once `const_panic` is stable
+                #[cfg(not(bootstrap))]
+                assert!(value <= ($max as usize));
+                #[cfg(bootstrap)]
                 [()][(value > ($max as usize)) as usize];
                 unsafe {
                     Self::from_u32_unchecked(value as u32)
@@ -133,7 +135,9 @@ macro_rules! newtype_index {
 
             #[inline]
             $v const fn from_u32(value: u32) -> Self {
-                // FIXME: replace with `assert!(value <= $max);` once `const_panic` is stable
+                #[cfg(not(bootstrap))]
+                assert!(value <= $max);
+                #[cfg(bootstrap)]
                 [()][(value > $max) as usize];
                 unsafe {
                     Self::from_u32_unchecked(value)