db_mysql: fix compile warning #612

> CC (gcc) [M db_mysql.so]		my_cmd.o
> In file included from /usr/include/string.h:25:0,
>                  from ../../lib/srdb2/../../str.h:24,
>                  from ../../lib/srdb2/db_gen.h:30,
>                  from ../../lib/srdb2/db_drv.h:29,
>                  from my_cmd.h:25,
>                  from my_cmd.c:33:
> /usr/include/features.h:148:3: warning: #warning "_BSD_SOURCE and _SVID_SOURCE are deprecated, use _DEFAULT_SOURCE" [-Wcpp]
>  # warning "_BSD_SOURCE and _SVID_SOURCE are deprecated, use _DEFAULT_SOURCE"

modules/db_mysql/my_cmd.c

@@ -29,6 +29,7 @@
 #endif
 #define _XOPEN_SOURCE_EXTENDED 1    /* solaris */
 #define _SVID_SOURCE 1 /* timegm */
+#define _DEFAULT_SOURCE 1 /* _SVID_SOURCE is deprecated */
 
 #include "my_cmd.h"