[NFC] Fixes -Wrange-loop-analysis warnings

This avoids new warnings due to D68912 adds -Wrange-loop-analysis to -Wall.

Differential Revision: https://reviews.llvm.org/D71857
diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
index cf3074d..6ed172bb 100644
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -2423,7 +2423,7 @@
 }
 
 void CodeGenModule::registerGlobalDtorsWithAtExit() {
-  for (const auto I : DtorsUsingAtExit) {
+  for (const auto &I : DtorsUsingAtExit) {
     int Priority = I.first;
     const llvm::TinyPtrVector<llvm::Function *> &Dtors = I.second;