[llvm] [SelectionDAG] Treat CopyFromReg as freezing the value (PR #85932)

[David Spickett via llvm-commits]

DavidSpickett wrote:

creduced example:
```
extern void f();
long double a, b, c, d;
void e() {
  if (a || c || d || b)
    f();
}
```


https://github.com/llvm/llvm-project/pull/85932