PR15633: Note that we are EnteringContext when parsing the nested name
specifier for an enumeration. Also fix a crash-on-invalid if a non-dependent
name specifier is used to declare an enum template.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@178502 91177308-0d34-0410-b5e6-96231b3b80d8