[modules] Deserialize CXXCtorInitializer list for a constructor lazily.

Previously we'd deserialize the list of mem-initializers for a constructor when
we deserialized the declaration of the constructor. That could trigger a
significant amount of unnecessary work (pulling in all base classes
recursively, for a start) and was causing problems for the modules buildbot due
to cyclic deserializations. We now deserialize these on demand.

This creates a certain amount of duplication with the handling of
CXXBaseSpecifiers; I'll look into reducing that next.

llvm-svn: 233052

clang/lib/Serialization/Module.cpp

@@ -38,6 +38,7 @@ ModuleFile::ModuleFile(ModuleKind Kind, unsigned Generation)
     SelectorLookupTableData(nullptr), SelectorLookupTable(nullptr),
     LocalNumDecls(0), DeclOffsets(nullptr), BaseDeclID(0),
     LocalNumCXXBaseSpecifiers(0), CXXBaseSpecifiersOffsets(nullptr),
+    LocalNumCXXCtorInitializers(0), CXXCtorInitializersOffsets(nullptr),
     FileSortedDecls(nullptr), NumFileSortedDecls(0),
     RedeclarationsMap(nullptr), LocalNumRedeclarationsInMap(0),
     ObjCCategoriesMap(nullptr), LocalNumObjCCategoriesInMap(0),