name lookup information have changed since deserialization. For a C++ modules
build, we do not need to re-emit the identifier into the serialized identifier
table if only the name lookup information has changed (and in all cases, we
don't need to re-emit the macro information if only the name lookup information
has changed).


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@259901 91177308-0d34-0410-b5e6-96231b3b80d8