is build_tools ignoring MAKEFLAGS?

[VeldoraTheDragon]

Hi
I'm currently building onlyoffice desktop editors via this PKGBUILD in the AUR:
https://aur.archlinux.org/cgit/aur.git/tree/PKGBUILD?h=onlyoffice

I've configured MAKEFLAGS in my makepkg.conf to only utilize 10 cores of my present 16 cores.
However, when observing the output of htop it utilizes all 16 cores for the build-process.

Is build_tools even using the MAKEFLAGS to limit the cpu-core usage?
If not, does build_tools have an option to limit cpu-usage?

Thanks.