‘sincos’ is a GNU extension. cogl-gles2-gears was using it without
defining _GNU_SOURCE so it was generating some annoying warnings. This
patch fixes it by making the example include config.h which will end
up defining _GNU_SOURCE.
In addition this patch adds a configure check for the function and
provides a fallback if it's not available.
https://bugzilla.gnome.org/show_bug.cgi?id=697330
Reviewed-by: Robert Bragg <robert@linux.intel.com>
(cherry picked from commit eb5c92952e1882c95cfd6debc69a2c9efff096b9)
95fe636a53
