gcc march and make threads

[Murbix]

Is there a way to pass arguments to gcc and make?
I would like to force gcc to user `march=native` cpu flag. Also wanted to rise build threads to 4. manually it is done by invoking `make -j4`. adding threads would cut build time significantly
Is this possible somehow when using custombuild?

 

[smtalk]

CustomBuild adds -j flag automatically without any customizations.