PR27513: When determining which declaration to put into an exported lookup

table for a module / PCH, never map from a normal declaration of a class to an
injected-class-name declaration (or vice versa). Those declarations live in
distinct lookup tables and should not be confused.

We really shouldn't be using a CXXRecordDecl to represent an
injected-class-name in the first place; I've filed PR27532 so we don't forget.

llvm-svn: 267632