When loading an identifier from an AST file solely for the purpose of
forming the identifier, e.g., as part of a selector or a declaration
name, don't actually deserialize any information about the
identifier. Instead, simply mark it "out-of-date" and we'll load the
the information on demand. 2% speedup on the modules testcase I'm
looking at; should also help PCH.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@173056 91177308-0d34-0410-b5e6-96231b3b80d8