I’d recommend just building code directly on the JTK1. However, cross-compilers compatible with this would be named similar to “arm-linux-gnueabihf”. I develop on Fedora and use Linaro tool chain. Look here for the most recent releases:
I’m not sure where the link is for download of the older 4.9 series.
I believe you can use that same compiler for u-boot, but most people would use the “arm-none-eabihf” compilers (note “none” replaces “linux” to imply bare metal). Documentation and downloads can be viewed here: