This patch set adding basic -march option support and feature test marco for vector extensions, and also extend the syntax of arch string for vector extensions, although that should change RISC-V ISA manual first would be better, but we don't got response[1] yet, and that will block whole vector extensions, so we decide fix that first.
[1] https://github.com/riscv/riscv-isa-manual/pull/718
