[Serialization] Avoid iterating Dense{Map,Set} to break determinism

in ASTWriter

It is bad to iterate Dense{Map,Set} in ASTWriter. Since the order in
Dense{Map, Set} is not stable. It may cause the produced BMI differ
even if we run the compiler twice without modifying any other thing.

Author: ChuanqiXu9

clang/include/clang/Serialization/ASTWriter.h

@@ -370,7 +370,7 @@ class ASTWriter : public ASTDeserializationListener,
   ///
   /// Only meaningful for standard C++ named modules. See the comments in
   /// createSignatureForNamedModule() for details.
-  llvm::DenseSet<Module *> TouchedTopLevelModules;
+  llvm::SetVector<Module *> TouchedTopLevelModules;
 
   /// An update to a Decl.
   class DeclUpdate {

clang/lib/Serialization/ASTWriter.cpp

@@ -4438,7 +4438,7 @@ void ASTWriter::GenerateSpecializationInfoLookupTable(
       Generator;
   LazySpecializationInfoLookupTrait Trait(*this);
 
-  llvm::DenseMap<unsigned, llvm::SmallVector<const NamedDecl *, 4>>
+  llvm::MapVector<unsigned, llvm::SmallVector<const NamedDecl *, 4>>
       SpecializationMaps;
 
   for (auto *Specialization : Specializations) {