Re: [PATCH 01/13] Nextstep: Use instancetype explicit return type

[Paul Eggert]

Oops, I spoke too quickly. This patch breaks the build on Ubuntu 16.04.2 LTS 
x86-64, with the following being the first symptom:

In file included from nsterm.m:48:0:
nsterm.h: At top level:
nsterm.h:447:4: error: unknown type name ‘instancetype’
 - (instancetype)menuDown: (id)sender;
    ^

Is that something you can fix? We need the Nextstep port to work with GNUstep as 
well as with macOS.

Looking backward, I see that even before the recent patches the build was 
already broken on Ubuntu 16.04.2 LTS, as follows:

nsfns.m: In function ‘Fns_set_mouse_absolute_pixel_position’:
nsfns.m:3101:3: error: unknown type name ‘CGPoint’
   CGPoint mouse_pos = CGPointMake(mouse_x, mouse_y);
   ^

Still, we shouldn't make things worse. I'll CC: this to Alan Third and Anders 
Lindgren to see whether they can advise.