[Bug target/115325] RVV vmulh and vmulhu unknown without -march, but vmul is known

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115325

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The correct way of doing this is to use `pragma GCC target` but that is not
supported on riscv yet ...