[builtins] Limit slow Promise.all tests to x64.

Bug: v8:7253
Change-Id: I1724fdac3668bcc05ff581113ac843ab5ef1def2
Reviewed-on: https://chromium-review.googlesource.com/977971Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52179}

test/mjsunit/mjsunit.status

@@ -105,7 +105,7 @@
   'migrations': [SKIP],
   'array-functions-prototype-misc': [PASS, SLOW, ['mode == debug', SKIP]],
   'compiler/regress-808472': [PASS, ['mode == debug', SKIP]],
-  'es6/promise-all-overflow-*': [PASS, SLOW, ['mode == debug', SKIP]],
+  'es6/promise-all-overflow-*': [PASS, SLOW, ['mode == debug or arch != x64', SKIP]],
 
   ##############################################################################
   # This test sets the umask on a per-process basis and hence cannot be