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1.53.0 broke ui/consts/const-eval/ub-*.rs tests on s390x (big-endian, 64-bit) (regression) #89577

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Probably because s390x is 64-bit big-endian not little-endian, e.g.:

Debian build log, warning several MB

sample
------------------------------------------
diff of 64bit.stderr:

6          |
7          = 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.
8          = note: the raw bytes of the constant (size: 8, align: 8) {
-                      01 00 00 00 00 00 00 00                         │ ........
+                      00 00 00 00 00 00 00 01                         │ ........
10                 }
11      
12      error[E0080]: it is undefined behavior to use this value

116        |
117        = 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.
118        = note: the raw bytes of the constant (size: 8, align: 4) {
-                      78 00 00 00 ff ff ff ff                         │ x.......
+                      00 00 00 78 ff ff ff ff                         │ ...x....
120                }
121     
122     error[E0080]: it is undefined behavior to use this value
test [ui] ui/consts/const-eval/ub-enum.rs ... FAILED
test [ui] ui/consts/const-eval/ub-int-array.rs ... FAILED
test [ui] ui/consts/const-eval/ub-nonnull.rs ... FAILED
test [ui] ui/consts/const-eval/ub-ref-ptr.rs ... FAILED
test [ui] ui/consts/const-eval/ub-uninhabit.rs ... FAILED
test [ui] ui/consts/const-eval/ub-wide-ptr.rs ... FAILED

These tests were fine in 1.52 so the culprit is probably #76881 @hameerabbasi . I will revert it in Debian for now.

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    C-bugCategory: This is a bug.O-SystemZTarget: SystemZ processors (s390x)P-mediumMedium priorityregression-from-stable-to-stablePerformance or correctness regression from one stable version to another.

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