GL: Add fallback debug layer

This is to improve debugging on older hardware that may not support
4.3 debug capabilities (like Macs).

This avoids sprinkling glGetErrors manually. This might still be needed
to find the root cause since not all functions are covered.

This overrides the functions pointers that GLEW have already init.

This is only enabled if using --debug-gpu option and the debug extension
are not available.

This also cleanup the usage of GLContext::debug_layer_support and use
wrapper to set object labels.

source/blender/gpu/opengl/gl_state.cc

@@ -30,6 +30,7 @@
 #include "glew-mx.h"
 
 #include "gl_context.hh"
+#include "gl_debug.hh"
 #include "gl_framebuffer.hh"
 #include "gl_texture.hh"