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

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

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

--- Comment #1 from Drea Pinski <pinskia at gcc dot gnu.org> ---
Even something like:
```
long f(long a)
{
    long t = 1234567890123;
    if (a) return t;
    return t+12;
}
```
Could be better optimized.