[Bug target/125765] `a ? CST0 : (CST0|CST1)` can be handled better for riscv

[law at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125765

--- Comment #2 from Jeffrey A. Law <law at gcc dot gnu.org> ---
I would expect anything with a nontrivial constant likely isn't handled well at
this time.