[Bug target/71338] [RL78] mulu instruction not used on G10

[olegendo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71338

--- Comment #5 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to DJ Delorie from comment #4)
> Sure, the only dependencies might be on binutils/gdb releases, but they
> support it and they're independent of gcc releases anyway.

As far as I know, binutils GAS does not check for mulu usage when compiling for
G10 and happily accepts it in e.g. inline asm blocks.  So I think it should be
OK from that side.  I'll backport r237566.