[AST] Use a reference in a range-based for

[Mordante]

Summary

This avoids unneeded copies when using a range-based for loops.

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

clang/lib/AST/ASTContext.cpp

structHasUniqueObjectRepresentations(const ASTContext &Context,
   const auto &Layout = Context.getASTRecordLayout(RD);
 
   int64_t CurOffsetInBits = 0;
   if (const auto *ClassDecl = dyn_cast<CXXRecordDecl>(RD)) {
     if (ClassDecl->isDynamicClass())
       return llvm::None;
 
     SmallVector<std::pair<QualType, int64_t>, 4> Bases;
-    for (const auto Base : ClassDecl->bases()) {
+    for (const auto &Base : ClassDecl->bases()) {
       // Empty types can be inherited from, and non-empty types can potentially
       // have tail padding, so just make sure there isn't an error.
       if (!isStructEmpty(Base.getType())) {
         llvm::Optional<int64_t> Size = structHasUniqueObjectRepresentations(
             Context, Base.getType()->castAs<RecordType>()->getDecl());
         if (!Size)
           return llvm::None;
         Bases.emplace_back(Base.getType(), Size.getValue());
       }
     }
 
     llvm::sort(Bases, [&](const std::pair<QualType, int64_t> &L,
                           const std::pair<QualType, int64_t> &R) {
       return Layout.getBaseClassOffset(L.first->getAsCXXRecordDecl()) <
              Layout.getBaseClassOffset(R.first->getAsCXXRecordDecl());
     });
 
-    for (const auto Base : Bases) {
+    for (const auto &Base : Bases) {
       int64_t BaseOffset = Context.toBits(
           Layout.getBaseClassOffset(Base.first->getAsCXXRecordDecl()));
       int64_t BaseSize = Base.second;
       if (BaseOffset != CurOffsetInBits)
         return llvm::None;
       CurOffsetInBits = BaseOffset + BaseSize;
     }
   }