makefiles/arch/riscv.inc.mk: Detect target triple
makefiles/arch/riscv.inc.mk: Detect target triple

This improves the target triple detection logic to include all possible target
triples of compilers that might be able to generate our binaries.

OlegHahm/RIOT,RIOT-OS/RIOT,ant9000/RIOT,kYc0o/RIOT,authmillenon/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,authmillenon/RIOT,jasonatran/RIOT,ant9000/RIOT,OlegHahm/RIOT,kaspar030/RIOT,miri64/RIOT,jasonatran/RIOT,miri64/RIOT,kaspar030/RIOT,authmillenon/RIOT,kYc0o/RIOT,miri64/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,OlegHahm/RIOT,kaspar030/RIOT,kaspar030/RIOT,kaspar030/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,kYc0o/RIOT,ant9000/RIOT,ant9000/RIOT,OTAkeys/RIOT,jasonatran/RIOT,jasonatran/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,miri64/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,ant9000/RIOT,OlegHahm/RIOT,kYc0o/RIOT,miri64/RIOT,kYc0o/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT