[wasm-simd] Fix byte order when setting mask values

Multi byte values get stored on native host order when
arrays are being constructed, however as Wasm is LE enforced,
they get reversed on BE machines during simd load. This causes
incorrect values loaded into vector registers.

This CL will force mask elements to be saved in byte sizes
to eliminate endianness issues.

Change-Id: I7f2e5017664234e01fc8b51a95cdd852a418b651
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2645586Reviewed-by: Zhi An Ng <zhin@chromium.org>
Commit-Queue: Milad Fa <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/master@{#72340}

test/cctest/wasm/test-run-wasm-simd.cc

@@ -801,26 +801,22 @@ WASM_SIMD_TEST_NO_LOWERING(I8x16SignSelect) {
 }
 
 WASM_SIMD_TEST_NO_LOWERING(I16x8SignSelect) {
-  std::array<int16_t, kSimd128Size / 2> selection = {0x8000, 0, -1, 0,
-                                                     0x8000, 0, -1, 0};
-  std::array<int8_t, kSimd128Size> mask;
-  memcpy(mask.data(), selection.data(), kSimd128Size);
+  std::array<int8_t, kSimd128Size> mask = {0, 0x80, 0, 0, -1, -1, 0, 0,
+                                           0, 0x80, 0, 0, -1, -1, 0, 0};
   RunSignSelect<int16_t>(execution_tier, lower_simd, kExprI16x8SignSelect,
                          kExprI16x8Splat, mask);
 }
 
 WASM_SIMD_TEST_NO_LOWERING(I32x4SignSelect) {
-  std::array<int32_t, kSimd128Size / 4> selection = {0x80000000, 0, -1, 0};
-  std::array<int8_t, kSimd128Size> mask;
-  memcpy(mask.data(), selection.data(), kSimd128Size);
+  std::array<int8_t, kSimd128Size> mask = {0,  0,  0,  0x80, 0, 0, 0, 0,
+                                           -1, -1, -1, -1,   0, 0, 0, 0};
   RunSignSelect<int32_t>(execution_tier, lower_simd, kExprI32x4SignSelect,
                          kExprI32x4Splat, mask);
 }
 
 WASM_SIMD_TEST_NO_LOWERING(I64x2SignSelect) {
-  std::array<int64_t, kSimd128Size / 8> selection = {0x8000000000000000, 0};
-  std::array<int8_t, kSimd128Size> mask;
-  memcpy(mask.data(), selection.data(), kSimd128Size);
+  std::array<int8_t, kSimd128Size> mask = {0, 0, 0, 0, 0, 0, 0, 0x80,
+                                           0, 0, 0, 0, 0, 0, 0, 0};
   RunSignSelect<int64_t>(execution_tier, lower_simd, kExprI64x2SignSelect,
                          kExprI64x2Splat, mask);
 }