Bug 1542963 - Fix undefined var 'defines' when use_defines_in_asflags is set. r=glandium

Lint python/mozbuild/{mozbuild,mozpack}.

Differential Revision: https://phabricator.services.mozilla.com/D26642

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

python/mozbuild/mozbuild/gn_processor.py

@@ -277,8 +277,8 @@ def process_gn_config(gn_config, srcdir, config, output, non_unified_sources,
             context_attrs['LOCAL_INCLUDES'] += [include]
 
         context_attrs['ASFLAGS'] = spec.get('asflags_mozilla', [])
-        if use_defines_in_asflags and defines:
-            context_attrs['ASFLAGS'] += ['-D' + d for d in defines]
+        if use_defines_in_asflags and context_attrs['DEFINES']:
+            context_attrs['ASFLAGS'] += ['-D' + d for d in context_attrs['DEFINES']]
         flags = [_f for _f in spec.get('cflags', []) if _f in mozilla_flags]
         if flags:
             suffix_map = {