deps: V8: revert e3cddbedb205

simdutf's `atomic_binary_to_base64` requires `std::atomic_ref`.
`std::atomic_ref` is only available in LLVM 19, which is only available
in Xcode 16.3, which is only available on macOS 15.

Refs: llvm/llvm-project#76647
Refs: v8/v8@e3cddbe

Author: targos

deps/v8/BUILD.bazel

@@ -4361,12 +4361,6 @@ cc_library(
   name = "simdutf",
   srcs = ["third_party/simdutf/simdutf.cpp"],
   hdrs = ["third_party/simdutf/simdutf.h"],
-  copts = select({
-        "@v8//bazel/config:is_clang": ["-std=c++20"],
-        "@v8//bazel/config:is_gcc": ["-std=gnu++2a"],
-        "@v8//bazel/config:is_windows": ["/std:c++20"],
-        "//conditions:default": [],
-    }),
 )
 
 v8_library(

deps/v8/src/builtins/builtins-typed-array.cc

@@ -818,16 +818,11 @@ BUILTIN(Uint8ArrayPrototypeToBase64) {
     //    is false.
     // 11. Return CodePointsToString(outAscii).
 
-    size_t simd_result_size;
-    if (uint8array->buffer()->is_shared()) {
-      simd_result_size = simdutf::atomic_binary_to_base64(
-          std::bit_cast<const char*>(uint8array->GetBuffer()->backing_store()),
-          length, reinterpret_cast<char*>(output->GetChars(no_gc)), alphabet);
-    } else {
-      simd_result_size = simdutf::binary_to_base64(
-          std::bit_cast<const char*>(uint8array->GetBuffer()->backing_store()),
-          length, reinterpret_cast<char*>(output->GetChars(no_gc)), alphabet);
-    }
+    // TODO(rezvan): Make sure to add a path for SharedArrayBuffers when
+    // simdutf library got updated. Also, add a test for it.
+    size_t simd_result_size = simdutf::binary_to_base64(
+        std::bit_cast<const char*>(uint8array->GetBuffer()->backing_store()),
+        length, reinterpret_cast<char*>(output->GetChars(no_gc)), alphabet);
     DCHECK_EQ(simd_result_size, output_length);
     USE(simd_result_size);
   }