Issue #1477 - Fix finding config.guess on builds not using MOZ_OBJDIR

* So far this seems to only affect Macintosh builds but other unix builds may be affected. Windows doesn't seem to be.
* This maintains consistency with other one-off file invocations and backwards compatibility with older comm setups

python/mozbuild/mozbuild/base.py

@@ -352,6 +352,13 @@ class MozbuildObject(ProcessExecutionMixin):
             return _config_guess_output[0]
 
         p = os.path.join(self.topsrcdir, 'build', 'autoconf', 'config.guess')
+        
+        # Try looking for mozilla, for comm-central
+        if not os.path.isfile(p):
+            p = os.path.join(self.topsrcdir, 'mozilla', 'build', 'autoconf', 'config.guess')
+
+        if not os.path.isfile(p):
+            p = os.path.join(self.topsrcdir, 'platform', 'build', 'autoconf', 'config.guess')
 
         # This is a little kludgy. We need access to the normalize_command
         # function. However, that's a method of a mach mixin, so we need a