You can find the information here. Suricata 5.x requires host RustC/Cargo (which I've added), and I don't know for sure, but I strongly suspect that I'm probably the first one to cross_compile 6.0.0beta1 since I'm hitting many of the same roadblocks I ran into with 5.x 
(AC_RUN_* and AC_FILE_* in configure can't be called while $cross_compiling, for example)
The good news is they have always been serious about fixing the issues they get, and this one seems no different.
If you want to test Suricata 5.0.3, grab both the rustup PR and the Suricata5 commit.