[Bug target/122018] x86 doesn't use BTS bitmanip instruction to both set and test bit

[uis9936 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122018

--- Comment #18 from uis <uis9936 at gmail dot com> ---
I still don't know if ix86_pre_reload_split() should be here, which I copied
from other insn_and_split.

I also noticed how fragile bts combine can be, here I can move one line and
both gcc 15 and trunk fail:

void g();
int f(int a, int b) {
    bool t = false;
    t = (a >> b) & 1;
    if(!t) {
        a = a | (1 << b);
        g();
    }
    return a;
}