Auto merge of #142008 - RalfJung:const-eval-error-here, r=oli-obk

const-eval error: always say in which item the error occurred

I don't see why "is this generic" should make a difference. It may be reasonable to key this on whether the error occurs in a `const fn` that was invoked by a const (making it non-obvious which constant it is) vs inside the body of the const.

r? `@oli-obk`

Author: bors

tests/fail/const-ub-checks.stderr

@@ -2,7 +2,7 @@ error[E0080]: accessing memory based on pointer with alignment ALIGN, but alignm
   --> tests/fail/const-ub-checks.rs:LL:CC
    |
 LL |     ptr.read();
-   |     ^^^^^^^^^^ evaluation of constant value failed here
+   |     ^^^^^^^^^^ evaluation of `UNALIGNED_READ` failed here
 
 note: erroneous constant encountered
   --> tests/fail/const-ub-checks.rs:LL:CC

tests/fail/erroneous_const2.stderr

@@ -2,7 +2,7 @@ error[E0080]: attempt to compute `5_u32 - 6_u32`, which would overflow
   --> tests/fail/erroneous_const2.rs:LL:CC
    |
 LL | const FOO: u32 = [X - Y, Y - X][(X < Y) as usize];
-   |                   ^^^^^ evaluation of constant value failed here
+   |                   ^^^^^ evaluation of `FOO` failed here
 
 note: erroneous constant encountered
   --> tests/fail/erroneous_const2.rs:LL:CC