When loading an identifier from an AST file solely for the purpose of

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 Instead, simply mark it "out-of-date" and we'll load the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.

llvm-svn: 173056