Thanks for your quick answer.
I tried building for Neo Air with arm-linux-gnueabihf-gcc and it works for me too without any error.
For Neo2 and/or Neo Plus2 I will try something that You mentioned to me or I will use branch 2017.03 till I can not build the another.
Thanks again.

Hi, I tried to build the latest U-Boot yesterday, followed by instructions here: Mainline U-boot Linux for H5 For building I used Ubuntu 17.10 because only this OS contains aarch64-linux-gnu version 6.x or more by default (or can install version 5.x, 6.x or 7.x). Unfortunately on Ubuntu 16.04 I got ...

There was an error message in your log: UIMAGE arch/arm/boot/uImage "mkimage" command not found - U-Boot images will not be built make[1]: *** [arch/arm/boot/uImage] Error 1 make: *** [uImage] Error 2 I am not sure, but I think that you need to install u-boot-tools because the mkimage is a...