as cannot do endbr64 instructions (too old)

hi misc@,

like the subject says, `as` in the base system cannot do endbr64
instructions. should it be updated?

background: i am maintaining hare for openbsd and we always have
to install "gas" from the "binutils" package because the normal one
is too old. i'd be nice if we don't depend on any packages from
ports and don't have some specific workarounds in hare just for
openbsd because "as" is too old.

if updating "as" is not an option, is there a way to invoke the
llvm assembler directly in the base system?

thanks.

- lorenz