[llvm] [Transforms] Use range-based for loops (NFC) (PR #97195)

[Kazu Hirata via llvm-commits]

================
@@ -226,9 +226,7 @@ static bool mergeConstants(Module &M) {
     // Now that we have figured out which replacements must be made, do them all
     // now.  This avoid invalidating the pointers in CMap, which are unneeded
     // now.
-    for (unsigned i = 0, e = SameContentReplacements.size(); i != e; ++i) {
-      GlobalVariable *Old = SameContentReplacements[i].first;
-      GlobalVariable *New = SameContentReplacements[i].second;
+    for (const auto &[Old, New] : SameContentReplacements) {
----------------
kazutakahirata wrote:

I just tried to drop `&`, but that resulted in:

```
llvm/lib/Transforms/IPO/ConstantMerge.cpp:229:21: error: loop variable '[Old, New]'
creates a copy from type 'std::pair<llvm::GlobalVariable *, llvm::GlobalVariable *>
const' [-Werror,-Wrange-loop-construct]
```


https://github.com/llvm/llvm-project/pull/97195