Your ROOT_URL in app.ini is https://src.whiteboxsystems.nl/ but you are visiting http://src.whiteboxsystems.nl/Whitebox/u-boot/commit/7651f8bdbba03bb0b4f241e2d2c4cb65b230bd56
You should set ROOT_URL correctly, otherwise the web may not work correctly.
What was suppose to be a stack variable was declared as a pointer,
overwriting random memory.
Also moved the libfdt.a requirement into the main Makefile. That is
The U-Boot Way.