[builtins] Temporary disable embedded builtins on s390 and ppc

Bug: v8:7571
Change-Id: Ifb59192ecefaa0f7968578a3b547b9e1fbe7c7d7
Reviewed-on: https://chromium-review.googlesource.com/971828
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52090}

BUILD.gn

@@ -70,7 +70,9 @@ declare_args() {
   v8_enable_embedded_builtins =
       v8_current_cpu != "x86" && v8_current_cpu != "mips" &&
       v8_current_cpu != "mipsel" && v8_current_cpu != "mips64" &&
-      v8_current_cpu != "mips64el" && (!is_win || is_clang)
+      v8_current_cpu != "mips64el" && v8_current_cpu != "ppc" &&
+      v8_current_cpu != "ppc64" && v8_current_cpu != "s390" &&
+      v8_current_cpu != "s390x" && (!is_win || is_clang)
 
   # Enable code-generation-time checking of types in the CodeStubAssembler.
   v8_enable_verify_csa = false