examples: Fix some main() function prototypes

examples/loading/clone_models/source/main.c

@@ -39,7 +39,7 @@ void Draw3DScene(void)
            NE_GetPolygonCount(), NE_GetVertexCount());
 }
 
-int main()
+int main(void)
 {
     irqEnable(IRQ_HBLANK);
     irqSet(IRQ_VBLANK, NE_VBLFunc);

examples/other/free_camera/source/main.c

@@ -20,7 +20,7 @@ void Draw3DScene(void)
     NE_ModelDraw(Model);
 }
 
-int main()
+int main(void)
 {
     irqEnable(IRQ_HBLANK);
     irqSet(IRQ_VBLANK, NE_VBLFunc);

examples/other/stylus_texture_drawing_rgba/source/main.c

@@ -16,7 +16,7 @@ void Draw3DScene(void)
     NE_2DDrawTexturedQuad(0, 0, 256, 256, 0, Material);
 }
 
-int main()
+int main(void)
 {
     irqEnable(IRQ_HBLANK);
     irqSet(IRQ_VBLANK, NE_VBLFunc);