[PATCH] PR target/98743: Fix ICE in convert_move for RISC-V

[Kito Cheng]

> >  - Check `TO` mode is not BLMmode before call store_expr, calling store_expr
> >    with BLKmode will cause ICE.
>
> How do you end up with a SUBREG_PROMOTED* of something that has bitsize of 0
> (GET_MODE_BITSIZE of BLKmode is 0, right)?

to_rtx is already having a mode other than BLKmode in this point,
it's SImode for riscv64*-*-*, so bitsize is 32 rather than 0.

I guess my comment isn't clear enough, the root cause why
`store_expr (from, to_rtx, 0, nontemporal, false)` ICE is
because `from` is still BLKmode here.

> That makes no sense.
>
>         Jakub
>