[embedded-builtins] Enable on all arches except x86 for benchmarks

This CL enables embedded builtins to get benchmark feedback. We need
this feedback to identify and address remaining performance problems.

Bug: v8:6666
Change-Id: I8f77f218e656b55ddabe1236eb2a1d14a5ac6233
Reviewed-on: https://chromium-review.googlesource.com/1105834Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53836}

BUILD.gn

@@ -77,10 +77,8 @@ declare_args() {
 
   # Enable embedded builtins.
   # TODO(jgruber,v8:6666): Support ia32 and maybe MSVC.
-  # TODO(jgruber,v8:6666): Enable for remaining architectures once performance
-  #                        regressions are addressed.
   v8_enable_embedded_builtins =
-      v8_use_snapshot && v8_current_cpu == "x64" && (!is_win || is_clang)
+      v8_use_snapshot && v8_current_cpu != "x86" && (!is_win || is_clang)
 
   # Enable code-generation-time checking of types in the CodeStubAssembler.
   v8_enable_verify_csa = false