MDEV-18439 Windows builds should have core_file=1 by default

sql/sys_vars.cc

@@ -474,7 +474,7 @@ bool check_has_super(sys_var *self, THD *thd, set_var *var)
 
 static Sys_var_bit Sys_core_file("core_file", "write a core-file on crashes",
           READ_ONLY GLOBAL_VAR(test_flags), NO_CMD_LINE,
-          TEST_CORE_ON_SIGNAL, DEFAULT(FALSE), NO_MUTEX_GUARD, NOT_IN_BINLOG,
+          TEST_CORE_ON_SIGNAL, DEFAULT(IF_WIN(TRUE,FALSE)), NO_MUTEX_GUARD, NOT_IN_BINLOG,
           0,0,0);
 
 static bool binlog_format_check(sys_var *self, THD *thd, set_var *var)