Rollup merge of #101486 - asquared31415:invalid_repr_list, r=estebank

Add list of recognized repr attributes to the unrecognized repr error

compiler/rustc_passes/src/check_attr.rs

@@ -1651,6 +1651,7 @@ impl CheckAttrVisitor<'_> {
                         E0552,
                         "unrecognized representation hint"
                     )
+                    .help("valid reprs are `C`, `align`, `packed`, `transparent`, `simd`, `i8`, `u8`, `i16`, `u16`, `i32`, `u32`, `i64`, `u64`, `i128`, `u128`, `isize`, `usize`")
                     .emit();
 
                     continue;