Android update and small improvements

-fixed code do cross compiling to android
-fixed build with GCC (workaround)
-added little benchmark
-several small fixes
-updated meson build (demos building, working with GCC, LDC and DMD)
-added some meson options
-added ImGUI bind for OpenGL3

demos/source/demos/space_invaders.d

@@ -1392,7 +1392,7 @@ struct UpgradeCollisionSystem
             if(space_invaders.shoot_grid.test(id, data.location[i], cast(ubyte)(0xFF)))
             {
                 Entity* entity = launcher.manager.getEntity(id);
-                if(entity.hasComponent(CShip.component_id))
+                if(entity && entity.hasComponent(CShip.component_id))
                 {
                     launcher.manager.sendEvent(id, EUpgrade());
                     launcher.manager.removeEntity(data.entity[i].id);