[ext-code-space] Disable external code space by default on arm64 Fuchsia

Bug: v8:11880, chromium:1292638
Change-Id: Ia457f391098aa2027988dae404948ab6f7fa8fab
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3450415
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Auto-Submit: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79012}

BUILD.gn

@@ -428,7 +428,8 @@ if (v8_enable_external_code_space == "") {
   v8_enable_external_code_space =
       v8_enable_pointer_compression &&
       (v8_current_cpu == "x64" ||
-       (target_os != "android" && v8_current_cpu == "arm64"))
+       (target_os != "android" && target_os != "fuchsia" &&
+        v8_current_cpu == "arm64"))
 }
 if (v8_enable_single_generation == "") {
   v8_enable_single_generation = v8_disable_write_barriers