Fixed Metal.

src/renderer_mtl.mm

@@ -678,6 +678,11 @@ namespace bgfx { namespace mtl
 			release(mem);
 		}
 
+		void setInternal(TextureHandle _handle, uintptr_t _ptr) BX_OVERRIDE
+		{
+			BX_UNUSED(_handle, _ptr);
+		}
+
 		void destroyTexture(TextureHandle _handle) BX_OVERRIDE
 		{
 			m_textures[_handle.idx].destroy();