Add the "quit" command as a way to terminate clang-query interactive sessions.

llvm-svn: 244206
diff --git a/clang-tools-extra/clang-query/Query.h b/clang-tools-extra/clang-query/Query.h
index f450570..109336a 100644
--- a/clang-tools-extra/clang-query/Query.h
+++ b/clang-tools-extra/clang-query/Query.h
@@ -32,6 +32,7 @@
   QK_Match,
   QK_SetBool,
   QK_SetOutputKind,
+  QK_Quit
 };
 
 class QuerySession;
@@ -76,6 +77,14 @@
   static bool classof(const Query *Q) { return Q->Kind == QK_Help; }
 };
 
+/// Query for "quit".
+struct QuitQuery : Query {
+  QuitQuery() : Query(QK_Quit) {}
+  bool run(llvm::raw_ostream &OS, QuerySession &QS) const override;
+
+  static bool classof(const Query *Q) { return Q->Kind == QK_Quit; }
+};
+
 /// Query for "match MATCHER".
 struct MatchQuery : Query {
   MatchQuery(const ast_matchers::dynamic::DynTypedMatcher &Matcher)