[_GLIBCXX_DEBUG] Clarify constness and state <unknown> entries.

	* src/c++11/debug.cc (print_field): Replace constness_names <unknown>
	entry with <unknown constness>. Replace state_names <unknown> entry with
	<unknown state>.

From-SVN: r277049

libstdc++-v3/ChangeLog

+2019-10-16  François Dumont  <fdumont@gcc.gnu.org>
+
+	* src/c++11/debug.cc (print_field): Replace constness_names <unknown>
+	entry with <unknown constness>. Replace state_names <unknown> entry with
+	<unknown state>.
+
 2019-10-11  Jonathan Wakely  <jwakely@redhat.com>
 
 	* include/Makefile.am: Add new header.

libstdc++-v3/src/c++11/debug.cc

@@ -721,7 +721,7 @@ namespace
 	    static const char*
 	      constness_names[_Error_formatter::__last_constness] =
 	      {
-		"<unknown>",
+		"<unknown constness>",
 		"constant",
 		"mutable"
 	      };
@@ -732,7 +732,7 @@ namespace
 	    static const char*
 	      state_names[_Error_formatter::__last_state] =
 	      {
-		"<unknown>",
+		"<unknown state>",
 		"singular",
 		"dereferenceable (start-of-sequence)",
 		"dereferenceable",