cmov: `cmoveq`/`cmovne` proptest failure on `powerpc-unknown-linux-gnu`

[tarcieri]

Possible big endian issue in the portable implementation? Discovered via #1295

The tests look like this, so only cmoveq/cmovne are impacted, whereas cmovz/cmovnz seem to be OK:

test i128::cmoveq_works ... ok
test i128::cmovne_works ... ok
test i128::cmovnz_works ... ok
test i128::cmovz_works ... ok
test i16::cmoveq_works ... ok
test i16::cmovne_works ... FAILED
test i16::cmovnz_works ... ok
test i16::cmovz_works ... ok
test i32::cmoveq_works ... FAILED
test i32::cmovne_works ... FAILED
test i32::cmovnz_works ... ok
test i32::cmovz_works ... ok
test i64::cmoveq_works ... FAILED
test i64::cmovne_works ... FAILED
test i64::cmovnz_works ... ok
test i64::cmovz_works ... ok
test i8::cmoveq_works ... ok
test i8::cmovne_works ... ok
test i8::cmovnz_works ... ok
test i8::cmovz_works ... ok
test u128::cmoveq_works ... ok
test u128::cmovne_works ... ok
test u128::cmovnz_works ... ok
test u128::cmovz_works ... ok
test u16::cmoveq_works ... FAILED
test u16::cmovne_works ... FAILED
test u16::cmovnz_works ... ok
test u16::cmovz_works ... ok
test u32::cmoveq_works ... FAILED
test u32::cmovne_works ... FAILED
test u32::cmovnz_works ... ok
test u32::cmovz_works ... ok
test u64::cmoveq_works ... FAILED
test u64::cmovne_works ... FAILED
test u64::cmovnz_works ... ok
test u64::cmovz_works ... ok
test u8::cmoveq_works ... ok
test u8::cmovne_works ... ok
test u8::cmovnz_works ... ok
test u8::cmovz_works ... ok

Here are the failing cases:

From https://github.com/RustCrypto/utils/actions/runs/20548544186/job/59022859407?pr=1295 while it lasts

---- i16::cmovne_works stdout ----
proptest: FileFailurePersistence::SourceParallel set, but failed to find lib.rs or main.rs
proptest: FileFailurePersistence::SourceParallel set, but failed to find lib.rs or main.rs
proptest: Saving this and future failures in /project/cmov/tests/proptests.proptest-regressions
proptest: If this test was run on a CI system, you may wish to add the following line to your copy of the file. (You may need to create it.)
cc a5a0bb6acbcc1a6dd696da12316cc50e05e58730422aebba3b6d7b1802920675

thread 'i16::cmovne_works' panicked at cmov/tests/proptests.rs:69:1:
Test failed: assertion failed: `(left == right)` 
  left: `1`,
 right: `0` at cmov/tests/proptests.rs:69.
minimal failing input: a = 12142, b = 14702, cond = 1
	successes: 70
	local rejects: 0
	global rejects: 0

note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

---- i32::cmoveq_works stdout ----
proptest: FileFailurePersistence::SourceParallel set, but failed to find lib.rs or main.rs

thread 'i32::cmoveq_works' panicked at cmov/tests/proptests.rs:69:1:
Test failed: assertion failed: `(left == right)` 
  left: `0`,
 right: `1` at cmov/tests/proptests.rs:69.
minimal failing input: a = 2036019054, b = -1456064146, cond = 1
	successes: 0
	local rejects: 0
	global rejects: 0


---- i32::cmovne_works stdout ----
proptest: FileFailurePersistence::SourceParallel set, but failed to find lib.rs or main.rs

thread 'i32::cmovne_works' panicked at cmov/tests/proptests.rs:69:1:
Test failed: assertion failed: `(left == right)` 
  left: `1`,
 right: `0` at cmov/tests/proptests.rs:69.
minimal failing input: a = 2036019054, b = -1456064146, cond = 1
	successes: 0
	local rejects: 0
	global rejects: 0


---- i64::cmoveq_works stdout ----
proptest: FileFailurePersistence::SourceParallel set, but failed to find lib.rs or main.rs
proptest: FileFailurePersistence::SourceParallel set, but failed to find lib.rs or main.rs
proptest: Saving this and future failures in /project/cmov/tests/proptests.proptest-regressions
proptest: If this test was run on a CI system, you may wish to add the following line to your copy of the file.
cc 193e10ca9e6470ec33310107af5258684e60390b8f2bf6fff6c52800089a3b41

thread 'i64::cmoveq_works' panicked at cmov/tests/proptests.rs:69:1:
Test failed: assertion failed: `(left == right)` 
  left: `0`,
 right: `1` at cmov/tests/proptests.rs:69.
minimal failing input: a = -5765293396052819090, b = -1494974746098486418, cond = 1
	successes: 107
	local rejects: 0
	global rejects: 0


---- i64::cmovne_works stdout ----
proptest: FileFailurePersistence::SourceParallel set, but failed to find lib.rs or main.rs

thread 'i64::cmovne_works' panicked at cmov/tests/proptests.rs:69:1:
Test failed: assertion failed: `(left == right)` 
  left: `1`,
 right: `0` at cmov/tests/proptests.rs:69.
minimal failing input: a = -5765293396052819090, b = -1494974746098486418, cond = 1
	successes: 0
	local rejects: 0
	global rejects: 0


---- u16::cmoveq_works stdout ----
proptest: FileFailurePersistence::SourceParallel set, but failed to find lib.rs or main.rs

thread 'u16::cmoveq_works' panicked at cmov/tests/proptests.rs:69:1:
Test failed: assertion failed: `(left == right)` 
  left: `0`,
 right: `1` at cmov/tests/proptests.rs:69.
minimal failing input: a = 12142, b = 14702, cond = 1
	successes: 0
	local rejects: 0
	global rejects: 0


---- u16::cmovne_works stdout ----
proptest: FileFailurePersistence::SourceParallel set, but failed to find lib.rs or main.rs

thread 'u16::cmovne_works' panicked at cmov/tests/proptests.rs:69:1:
Test failed: assertion failed: `(left == right)` 
  left: `1`,
 right: `0` at cmov/tests/proptests.rs:69.
minimal failing input: a = 12142, b = 14702, cond = 1
	successes: 0
	local rejects: 0
	global rejects: 0


---- u32::cmoveq_works stdout ----
proptest: FileFailurePersistence::SourceParallel set, but failed to find lib.rs or main.rs

thread 'u32::cmoveq_works' panicked at cmov/tests/proptests.rs:69:1:
Test failed: assertion failed: `(left == right)` 
  left: `0`,
 right: `1` at cmov/tests/proptests.rs:69.
minimal failing input: a = 2036019054, b = 2838903150, cond = 1
	successes: 0
	local rejects: 0
	global rejects: 0


---- u32::cmovne_works stdout ----
proptest: FileFailurePersistence::SourceParallel set, but failed to find lib.rs or main.rs

thread 'u32::cmovne_works' panicked at cmov/tests/proptests.rs:69:1:
Test failed: assertion failed: `(left == right)` 
  left: `1`,
 right: `0` at cmov/tests/proptests.rs:69.
minimal failing input: a = 2036019054, b = 2838903150, cond = 1
	successes: 0
	local rejects: 0
	global rejects: 0


---- u64::cmoveq_works stdout ----
proptest: FileFailurePersistence::SourceParallel set, but failed to find lib.rs or main.rs

thread 'u64::cmoveq_works' panicked at cmov/tests/proptests.rs:69:1:
Test failed: assertion failed: `(left == right)` 
  left: `0`,
 right: `1` at cmov/tests/proptests.rs:69.
minimal failing input: a = 12681450677656723566, b = 16946642025689120366, cond = 1
	successes: 0
	local rejects: 0
	global rejects: 0


---- u64::cmovne_works stdout ----
proptest: FileFailurePersistence::SourceParallel set, but failed to find lib.rs or main.rs

thread 'u64::cmovne_works' panicked at cmov/tests/proptests.rs:69:1:
Test failed: assertion failed: `(left == right)` 
  left: `1`,
 right: `0` at cmov/tests/proptests.rs:69.
minimal failing input: a = 12681450677656723566, b = 16946642025689120366, cond = 1
	successes: 0
	local rejects: 0
	global rejects: 0

[tarcieri]

#1299 adds a simple regression test which trivially reproduces it without proptest