playing around with libopencm3 on an inexpensive gd32 riscv board

Any GCC-based RISC-V toolchain should work. This has been tested with:

• riscv-sifive-elf-gcc: just works™
• riscv64-elf-gcc: you must add export PREFIX:=riscv64-elf- to the Makefile (or specify that variable in the environment)