Fix infinite recursion in OMP clause pretty-printing, default label

	gcc/
	* tree-pretty-print.c (dump_omp_clause): Make default case
	gcc_unreachable.

From-SVN: r266740

gcc/ChangeLog

+2018-12-03  Julian Brown  <julian@codesourcery.com>
+
+	* tree-pretty-print.c (dump_omp_clause): Make default case
+	gcc_unreachable.
+
 2018-12-03  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/88301

gcc/tree-pretty-print.c

@@ -1180,9 +1180,7 @@ dump_omp_clause (pretty_printer *pp, tree clause, int spc, dump_flags_t flags)
       break;
 
     default:
-      /* Should never happen.  */
-      dump_generic_node (pp, clause, spc, flags, false);
-      break;
+      gcc_unreachable ();
     }
 }