[Bug rtl-optimization/124020] Improve bitmanip recognition for riscv

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124020

--- Comment #4 from Jeffrey A. Law <law at gcc dot gnu.org> ---
And yet another from 500.perlbench:

void shafinish(unsigned char *block, int blockcnt)
{
        block[blockcnt] |= (0x01 << (blockcnt));    // ->    (bset)
        block[blockcnt] &= ~(0x01 << (blockcnt)); //  ->  (bclr)
}