Nitpicky refactoring -- use of nullptr and auto, made a bit more const-correct. No functional changes intended.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@206491 91177308-0d34-0410-b5e6-96231b3b80d8
Add missing serialization code for one of the CXXRecordDecl definition flags.


git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@206493 91177308-0d34-0410-b5e6-96231b3b80d8
Fix comment.


git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@206494 91177308-0d34-0410-b5e6-96231b3b80d8