Fix compiling warnings in OpenMP declare mapper codegen

[lildmh]

Summary

This patch fixed the compiling warnings that L is not a reference.

[grokos]

I can confirm the warnings are gone with this fix.

[lildmh]

Thanks George!

clang/lib/CodeGen/CGOpenMPRuntime.cpp

void generateAllInfo(MapCombinedInfoTy &CombinedInfo) const {
     const auto *CurExecDir = CurDir.get<const OMPExecutableDirective *>();
     for (const auto *C : CurExecDir->getClausesOfKind<OMPMapClause>())
       for (const auto L : C->component_lists()) {
         InfoGen(std::get<0>(L), std::get<1>(L), C->getMapType(),
                 C->getMapTypeModifiers(), /*ReturnDevicePointer=*/false,
                 C->isImplicit(), std::get<2>(L));
       }
     for (const auto *C : CurExecDir->getClausesOfKind<OMPToClause>())
-      for (const auto &L : C->component_lists()) {
+      for (const auto L : C->component_lists()) {
         InfoGen(std::get<0>(L), std::get<1>(L), OMPC_MAP_to, llvm::None,
                 /*ReturnDevicePointer=*/false, C->isImplicit(), std::get<2>(L));
       }
     for (const auto *C : CurExecDir->getClausesOfKind<OMPFromClause>())
-      for (const auto &L : C->component_lists()) {
+      for (const auto L : C->component_lists()) {
         InfoGen(std::get<0>(L), std::get<1>(L), OMPC_MAP_from, llvm::None,
                 /*ReturnDevicePointer=*/false, C->isImplicit(), std::get<2>(L));
       }
 
     // Look at the use_device_ptr clause information and mark the existing map
     // entries as such. If there is no map information for an entry in the
     // use_device_ptr list, we create one with map type 'alloc' and zero size
     // section. It is the user fault if that was not mapped before. If there is
     // no map information and the pointer is a struct member, then we defer the
     // emission of that entry until the whole struct has been processed.
     llvm::MapVector<const ValueDecl *, SmallVector<DeferredDevicePtrEntryTy, 4>>
         DeferredInfo;
 
     for (const auto *C :
          CurExecDir->getClausesOfKind<OMPUseDevicePtrClause>()) {
-      for (const auto &L : C->component_lists()) {
+      for (const auto L : C->component_lists()) {
         OMPClauseMappableExprCommon::MappableExprComponentListRef Components =
             std::get<1>(L);
         assert(!Components.empty() &&
                "Not expecting empty list of components!");
         const ValueDecl *VD = Components.back().getAssociatedDeclaration();
         VD = cast<ValueDecl>(VD->getCanonicalDecl());
         const Expr *IE = Components.back().getAssociatedExpression();
         // If the first component is a member expression, we have to look into