[ext-code-space] Enable external code space on x64 and desktop arm64

This is a reland #3. The fixes were landed separately.

Perf Sheriffs: this CL might regress some benchmarks while improving
the others.

Bug: v8:11880
Change-Id: I8ed5bf59360649718960dc34c06015ee6ff1532a
Cq-Include-Trybots: luci.v8.try:v8_android_arm64_compile_dbg
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3422643Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78854}

BUILD.gn

@@ -412,7 +412,12 @@ if (v8_enable_short_builtin_calls == "") {
       v8_current_cpu == "x64" || (!is_android && v8_current_cpu == "arm64")
 }
 if (v8_enable_external_code_space == "") {
-  v8_enable_external_code_space = false
+  # Can't use !is_android here, because Torque toolchain is affected by
+  # the value of this flag but actually runs on the host side.
+  v8_enable_external_code_space =
+      v8_enable_pointer_compression &&
+      (v8_current_cpu == "x64" ||
+       (target_os != "android" && v8_current_cpu == "arm64"))
 }
 if (v8_enable_single_generation == "") {
   v8_enable_single_generation = v8_disable_write_barriers