[Bug target/104853] [RISC-V] -march=rv64g not including extension Zifencei

[i at rvalue dot moe via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104853

--- Comment #7 from rvalue <i at rvalue dot moe> ---
Well, I've found something that could be problematic here:

https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/config/riscv/arch-canonicalize;h=49a6204b9cb64cb0e375c6003c423bf115a0a8a6;hb=HEAD#l60

It's never updated in ISA spec version bumping.