The error recovery path in _Pragma attempted to lex past the non-string
literal token and then lex past a closing right paren if it exists.
However, this path wasn't careful in the face of EOF.
This fixes PR20662.
I think you should also stop at EOD and EOM (that is, tok::eod and tok::annot_module_*).
I landed a change like this in r215672, but I don't have mail for it yet... Not sure what's up.
Superseded by rL215672.