[llvm] [CodeGen] Use a range-based for loop (NFC) (PR #97177)

[Kazu Hirata via llvm-commits]

kazutakahirata wrote:

> Isn't that loop just a `find_first_of()`?

It is.  If we save the iterator range to a temporary variable, it may be doable.  That is:

```
if (MI && MI->isInlineAsm())
  MI->emitError(...);
else if (MI)
  MI->emitError(...);
```

would become something like:

```
auto RegInstrs = MRI->reg_instructions(VirtReg->reg());
auto MI = llvm::find_if(RegInstrs, [&](const MachineInstr &MIR) {
  return MIR->isInlineAsm();
});
if (MI != RegInstrs.end())
  MI->emitError(...);
else if (!RegInstrs.empty())
  std::prev(RegInstrs.end())->emitError(...);
```

I sort of like the original code because `MI` encodes everything we need.

https://github.com/llvm/llvm-project/pull/97177