Fix ub-int-array test for big-endian platforms

As of commit 7767cbb,
the tests/ui/consts/const-eval/ub-int-array.rs test is
failing on big-endian platforms (in particular s390x),
as the stderr output contains a hex dump that depends
on endianness.

Since this point intentionally verifies the hex dump to
check the uninitialized byte markers, I think we should
not simply standardize away the hex dump as is done with
some of the other tests in this directory.

However, most of the test is already endian-independent.
The only exception is one line of hex dump, which can
also be made endian-independent by choosing appropriate
constants in the source code.

Since the 32bit and 64bit stderr outputs were already
(and remain) identical, I've merged them and removed
the stderr-per-bitwidth marker.

Fixes (again) rust-lang#105383.

Author: uweigand

tests/ui/consts/const-eval/ub-int-array.64bit.stderr

@@ -1,4 +1,3 @@
-// stderr-per-bitwidth
 //! Test the "array of int" fast path in validity checking, and in particular whether it
 //! points at the right array element.
 
@@ -19,7 +18,12 @@ impl<T: Copy> MaybeUninit<T> {
 const UNINIT_INT_0: [u32; 3] = unsafe {
     //~^ ERROR it is undefined behavior to use this value
     //~| invalid value at [0]
-    mem::transmute([MaybeUninit { uninit: () }, MaybeUninit::new(1), MaybeUninit::new(2)])
+    mem::transmute([
+        MaybeUninit { uninit: () },
+        // Constants chosen to achieve endianness-independent hex dump.
+        MaybeUninit::new(0x11111111),
+        MaybeUninit::new(0x22222222),
+    ])
 };
 const UNINIT_INT_1: [u32; 3] = unsafe {
     //~^ ERROR it is undefined behavior to use this value

tests/ui/consts/const-eval/ub-int-array.rs

@@ -1,16 +1,16 @@
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-int-array.rs:19:1
+  --> $DIR/ub-int-array.rs:18:1
    |
 LL | const UNINIT_INT_0: [u32; 3] = unsafe {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [0]: encountered uninitialized memory, but expected an integer
    |
    = note: The rules on what exactly is undefined behavior aren't clear, so this check might be overzealous. Please open an issue on the rustc repository if you believe it should not be considered undefined behavior.
    = note: the raw bytes of the constant (size: 12, align: 4) {
-               __ __ __ __ 01 00 00 00 02 00 00 00             │ ░░░░........
+               __ __ __ __ 11 11 11 11 22 22 22 22             │ ░░░░....""""
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-int-array.rs:24:1
+  --> $DIR/ub-int-array.rs:28:1
    |
 LL | const UNINIT_INT_1: [u32; 3] = unsafe {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [1]: encountered uninitialized memory, but expected an integer
@@ -21,7 +21,7 @@ LL | const UNINIT_INT_1: [u32; 3] = unsafe {
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/ub-int-array.rs:42:1
+  --> $DIR/ub-int-array.rs:46:1
    |
 LL | const UNINIT_INT_2: [u32; 3] = unsafe {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at [2]: encountered uninitialized memory, but expected an integer