Failed test HwyInterleavedTestGroup/HwyInterleavedTest.TestAllLoadStoreInterleaved4/EMU128 with gcc 15.1.1

Hello,

there is failed test reported by a Gentoo maintainer:
https://bugs.gentoo.org/960397

All test passed with gcc 14.3.0, but after upgrading gcc to version 15.1.1_p20250705-r1, there is a failed test:

highway 1.2.0:

```
775/1661 Test: HwyInterleavedTestGroup/HwyInterleavedTest.TestAllLoadStoreInterleaved4/EMU128 # GetParam() = 2305843009213693952
Command: "/var/tmp/portage/dev-cpp/highway-1.2.0/work/highway-1.2.0_build-abi_x86_64.amd64/tests/interleaved_test" "--gtest_filter=HwyInterleavedTestGroup/HwyInterleavedTest.TestAllLoadStoreInterleaved4/EMU128" "--gtest_also_run_disabled_tests"
Directory: /var/tmp/portage/dev-cpp/highway-1.2.0/work/highway-1.2.0_build-abi_x86_64.amd64
"HwyInterleavedTestGroup/HwyInterleavedTest.TestAllLoadStoreInterleaved4/EMU128 # GetParam() = 2305843009213693952" start time: Jul 20 10:16 CEST
Output:
----------------------------------------------------------
Running main() from /var/tmp/portage/dev-cpp/gtest-1.14.0-r2/work/googletest-1.14.0/googletest/src/gtest_main.cc
Note: Google Test filter = HwyInterleavedTestGroup/HwyInterleavedTest.TestAllLoadStoreInterleaved4/EMU128
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from HwyInterleavedTestGroup/HwyInterleavedTest
[ RUN ] HwyInterleavedTestGroup/HwyInterleavedTest.TestAllLoadStoreInterleaved4/EMU128

u64x2 expect [0+ ->]:
0x0000000000000027,0x0000000000000038,
u64x2 actual [0+ ->]:
0x0000003800000004,0x0000000000000038,
Abort at interleaved_test.cc:148: EMU128, u64x2 lane 0 mismatch: expected '0x0000000000000027', got '0x0000003800000004'.

Test time = 0.01 sec
----------------------------------------------------------
Test Failed.
"HwyInterleavedTestGroup/HwyInterleavedTest.TestAllLoadStoreInterleaved4/EMU128 # GetParam() = 2305843009213693952" end time: Jul 20 10:16 CEST
"HwyInterleavedTestGroup/HwyInterleavedTest.TestAllLoadStoreInterleaved4/EMU128 # GetParam() = 2305843009213693952" time elapsed: 00:00:00
----------------------------------------------------------
```

highway from git:

```
852/1969 Test: HwyInterleavedTestGroup/HwyInterleavedTest.TestAllLoadStoreInterleaved4/EMU128 # GetParam() = 2305843009213693952
Command: "/var/tmp/portage/dev-cpp/highway-9999/work/highway-9999_build-abi_x86_64.amd64/tests/interleaved_test" "--gtest_filter=HwyInterleavedTestGroup/HwyInterleavedTest.TestAllLoadStoreInterleaved4/EMU128" "--gtest_also_run_disabled_tests"
Directory: /var/tmp/portage/dev-cpp/highway-9999/work/highway-9999_build-abi_x86_64.amd64
"HwyInterleavedTestGroup/HwyInterleavedTest.TestAllLoadStoreInterleaved4/EMU128 # GetParam() = 2305843009213693952" start time: Jul 20 11:02 CEST
Output:
----------------------------------------------------------
Running main() from /var/tmp/portage/dev-cpp/gtest-1.14.0-r2/work/googletest-1.14.0/googletest/src/gtest_main.cc
Note: Google Test filter = HwyInterleavedTestGroup/HwyInterleavedTest.TestAllLoadStoreInterleaved4/EMU128
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from HwyInterleavedTestGroup/HwyInterleavedTest
[ RUN ] HwyInterleavedTestGroup/HwyInterleavedTest.TestAllLoadStoreInterleaved4/EMU128

u64x2 expect [0+ ->]:
0x0000000000000027,0x0000000000000038,
u64x2 actual [0+ ->]:
0x0000003800000004,0x0000000000000038,
Abort at interleaved_test.cc:157: EMU128, u64x2 lane 0 mismatch: expected '0x0000000000000027', got '0x0000003800000004'.

Test time = 0.00 sec
----------------------------------------------------------
Test Failed.
"HwyInterleavedTestGroup/HwyInterleavedTest.TestAllLoadStoreInterleaved4/EMU128 # GetParam() = 2305843009213693952" end time: Jul 20 11:02 CEST
"HwyInterleavedTestGroup/HwyInterleavedTest.TestAllLoadStoreInterleaved4/EMU128 # GetParam() = 2305843009213693952" time elapsed: 00:00:00
----------------------------------------------------------
```

Start with the failing HwyInterleavedTestGroup/HwyInterleavedTest.TestAllLoadStoreInterleaved4/EMU128 case in tests/interleaved_test.cc, around the reported assertion lines 148 or 157. Reproduce the filtered test with GCC 15.1.1 and compare it with GCC 14.3.0, then trace the interleaved load/store behavior involved. Done means the test passes correctly with the newer compiler without weakening the assertion.

Written by the indexing model from the issue text.