If you're building v18 you have to enable developer mode to get access to one of the per-requisite packages.
If you do a search for tgt in make menuconfig it will show you all the per-requisite packages you will need and if they are enabled. Just follow the chain and enable them one by one until they all say [y]. Some of the required packages also have per-requisites that need to be enabled first. I gave up because I couldn't figure out how to enable developer mode to get the options to show for one of the packages. As far as x86 and any differences, I haven't the slightest so you're on your own with that.