Bug 1515528 - Disable accessibility on aarch64-windows. r=dmajor,chmanchester

Depends on D15265

Differential Revision: https://phabricator.services.mozilla.com/D15266

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

browser/config/mozconfigs/win64-aarch64/common-win64

@@ -2,6 +2,3 @@
 
 ac_add_options --target=aarch64-windows-mingw32
 ac_add_options --host=x86_64-pc-mingw32
-
-# Accessibility doesn't work.
-ac_add_options --disable-accessibility

toolkit/moz.configure

@@ -1131,9 +1131,17 @@ set_config('MIDL_FLAGS', midl_flags)
 # Accessibility
 # ==============================================================
 
-option('--disable-accessibility', help='Disable accessibility support')
+@depends(target)
+def a11y_default(target):
+    # Accessibility doesn't work on aarch64-windows yet.
+    if target.kernel == 'WINNT' and target.cpu == 'aarch64':
+        return False
+    return True
 
-@depends('--disable-accessibility', check_for_midl, midl, c_compiler)
+option('--enable-accessibility',
+       default=a11y_default, help='{Enable|Disable} accessibility support')
+
+@depends('--enable-accessibility', check_for_midl, midl, c_compiler)
 def accessibility(value, check_for_midl, midl, c_compiler):
     enabled = bool(value)