Bug 1528621 - Disable ionmonkey on aarch64 as originally intended. r=dmajor

Differential Revision: https://phabricator.services.mozilla.com/D21492

--HG--
extra : moz-landing-system : lando

modules/libpref/init/all.js

@@ -1460,7 +1460,7 @@ pref("javascript.options.unboxed_objects",  false);
 pref("javascript.options.baselinejit",      true);
 //Duplicated in JitOptions - ensure both match.
 pref("javascript.options.baselinejit.threshold", 10);
-#ifdef _ARM64_
+#ifdef NO_ION
 pref("javascript.options.ion",              false);
 #else
 pref("javascript.options.ion",              true);

modules/libpref/moz.build

@@ -49,6 +49,9 @@ DEFINES['MOZ_WIDGET_TOOLKIT'] = CONFIG['MOZ_WIDGET_TOOLKIT']
 if CONFIG['MOZ_ENABLE_WEBRENDER']:
     DEFINES['MOZ_ENABLE_WEBRENDER'] = True
 
+if CONFIG['CPU_ARCH'] == 'aarch64':
+    DEFINES['NO_ION'] = True
+
 FINAL_TARGET_PP_FILES += [
     'greprefs.js',
 ]