yy_fatal_error calls exit(), so it should be declared
noreturn (improves optimisation of things that call it
and makes -Wmissing-noreturn happy).

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=189784

--- flex-2.5.35/flex.skl
+++ flex-2.5.35/flex.skl
@@ -729,9 +729,13 @@ m4_ifdef( [[M4_YY_NOT_IN_HEADER]],
 [[
 static yy_state_type yy_get_previous_state M4_YY_PARAMS( M4_YY_PROTO_ONLY_ARG );
 static yy_state_type yy_try_NUL_trans M4_YY_PARAMS( yy_state_type current_state  M4_YY_PROTO_LAST_ARG);
 static int yy_get_next_buffer M4_YY_PARAMS( M4_YY_PROTO_ONLY_ARG );
+#ifdef __GNUC__
+static void yy_fatal_error M4_YY_PARAMS( yyconst char msg[] M4_YY_PROTO_LAST_ARG ) __attribute__((noreturn));
+#else
 static void yy_fatal_error M4_YY_PARAMS( yyconst char msg[] M4_YY_PROTO_LAST_ARG );
+#endif
 ]])
 
 %endif