crt: tests: update t__sys_errlist

Previously, this test would simply print an error message if `_sys_errlist`
returns `NULL`. Instead, exit with non-zero to signal an error.

Signed-off-by: Kirill Makurin <maiddaisuki@outlook.com>
Signed-off-by: LIU Hao <lh_mouse@126.com>

mingw-w64-crt/testcases/t__sys_errlist.c

diff --git a/mingw-w64-crt/testcases/t__sys_errlist.c b/mingw-w64-crt/testcases/t__sys_errlist.c
index 1bb4ff8..bff2d7f 100644
--- a/mingw-w64-crt/testcases/t__sys_errlist.c
+++ b/mingw-w64-crt/testcases/t__sys_errlist.c
@@ -10,10 +10,12 @@
 {
   char **s = (char **) _sys_errlist;
 
-  if (s)
+  if (s) {
     printf ("Msg 0: %s\n", s[0]);
-  else
+  } else {
     printf ("Error list empty.\n");
+    _exit (EXIT_FAILURE);
+  }
 
   return 0;
 }