MDEV-11499 mysqltest, Windows : improve diagnostics if server fails to shutdown

Create minidump when server fails to shutdown. If process is being
debugged, cause a debug break.

Moves some code which is part of safe_kill into mysys, as both safe_kill,
and mysqltest produce minidumps on different timeouts.

Small cleanup in wait_until_dead() - replace inefficient loop with a single
wait.

include/my_minidump.h

@@ -0,0 +1,25 @@
+/* Copyright (c) 2021, MariaDB Corporation
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; version 2 of the License.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA */
+
+#include <windows.h>
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+BOOL my_create_minidump(DWORD pid, BOOL verbose);
+
+#ifdef __cplusplus
+}
+#endif