march option is actually a target triple

[cesarus777]

Reproduced on 1.0

Snippy -march option is actually target triple. According to RISC-V toolchain convention -march=rv64gc must be ok, but in snippy to specify rv64gc I need to set -march=riscv64 and -mattr=+m,+a,+f,+d,+c,+Zifencei,+Zicsr and this is a real hell and quite annoying. I would very appreciate if you fix this.