Master warnings pending in "make check"

[shakaran]

Running make check I get the following warnings, that probably it is good to fix at some point:

mypaint-surface.c:119: Warning: MyPaint: mypaint_surface_end_atomic: invalid return annotation
mypaint-rectangle.h:35: Warning: MyPaint: mypaint_rectangle_copy: return value: Invalid non-constant return of bare structure or union; register as boxed type or (skip)
mypaint-brush.c:128: Warning: MyPaint: mypaint_brush_new: return value: Invalid non-constant return of bare structure or union; register as boxed type or (skip)
mypaint-brush.c:128: Warning: MyPaint: mypaint_brush_new: return value: Invalid non-constant return of bare structure or union; register as boxed type or (skip)
mypaint-fixed-tiled-surface.h:30: Warning: MyPaint: mypaint_fixed_tiled_surface_interface: return value: Invalid non-constant return of bare structure or union; register as boxed type or (skip)
mypaint-fixed-tiled-surface.h:20: Warning: MyPaint: mypaint_fixed_tiled_surface_new: return value: Invalid non-constant return of bare structure or union; register as boxed type or (skip)
mypaint-fixed-tiled-surface.h:20: Warning: MyPaint: mypaint_fixed_tiled_surface_new: return value: Invalid non-constant return of bare structure or union; register as boxed type or (skip)