Heating issue: Resets under load

Building e.g. mesa like

git clone https://source.puri.sm/Librem5/mesa.git
cd mesa
meson --buildtype=debug -Dgallium-drivers=imx,etnaviv -Ddri-drivers= -Dvulkan-drivers=  . _build
ninja -C _build

makes the board reset after some time. Maybe due to heating. U-boot has

Commercial temperature grade (0C to 95C) at 73C

I'm running CPU up but without fan.