Thank you for your response.
So, I just need to wait next build?
unfortunately there seems to be another unrelated error (unrecognized compiler flags) in another package that also causes the build to fail. maybe best open a bug report too 
If you want I open a bug report, please, give me more informations 
Which package cause problem?
looks like this is a problem in the vboot_reference build. seems specific to mobile-nixos since it builds in nixos-unstable
https://hydra.nixos.org/build/213206486
New build success! 
Is it work for you?
I installed Tow-Boot and uses “dd” to copy the image to SD.
Do you want I open a new topic?
yes. can’t answer anything specific to mobile nixos anyway, never used the thing.