Rollup merge of rust-lang#154512 - GrigorenkoPV:alignment/const, r=scottmcm

Constify comparisons and `Clone` for `core::mem::Alignment`

As suggested in rust-lang#153261 (comment)

Author: JonathanBrouwer

library/core/src/mem/alignment.rs

@@ -11,7 +11,8 @@ use crate::{cmp, fmt, hash, mem, num};
 /// Note that particularly large alignments, while representable in this type,
 /// are likely not to be supported by actual allocators and linkers.
 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
-#[derive(Copy, Clone, PartialEq, Eq)]
+#[derive(Copy)]
+#[derive_const(Clone, PartialEq, Eq)]
 #[repr(transparent)]
 pub struct Alignment {
     // This field is never used directly (nor is the enum),
@@ -303,15 +304,17 @@ impl const From<Alignment> for usize {
 }
 
 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
-impl cmp::Ord for Alignment {
+#[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
+impl const cmp::Ord for Alignment {
     #[inline]
     fn cmp(&self, other: &Self) -> cmp::Ordering {
         self.as_nonzero_usize().cmp(&other.as_nonzero_usize())
     }
 }
 
 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
-impl cmp::PartialOrd for Alignment {
+#[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
+impl const cmp::PartialOrd for Alignment {
     #[inline]
     fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
         Some(self.cmp(other))
@@ -336,7 +339,8 @@ impl const Default for Alignment {
 }
 
 #[cfg(target_pointer_width = "16")]
-#[derive(Copy, Clone, PartialEq, Eq)]
+#[derive(Copy)]
+#[derive_const(Clone, PartialEq, Eq)]
 #[repr(usize)]
 enum AlignmentEnum {
     _Align1Shl0 = 1 << 0,
@@ -358,7 +362,8 @@ enum AlignmentEnum {
 }
 
 #[cfg(target_pointer_width = "32")]
-#[derive(Copy, Clone, PartialEq, Eq)]
+#[derive(Copy)]
+#[derive_const(Clone, PartialEq, Eq)]
 #[repr(usize)]
 enum AlignmentEnum {
     _Align1Shl0 = 1 << 0,
@@ -396,7 +401,8 @@ enum AlignmentEnum {
 }
 
 #[cfg(target_pointer_width = "64")]
-#[derive(Copy, Clone, PartialEq, Eq)]
+#[derive(Copy)]
+#[derive_const(Clone, PartialEq, Eq)]
 #[repr(usize)]
 enum AlignmentEnum {
     _Align1Shl0 = 1 << 0,