Add definition of _DEFAULT_SOURCE.

Since glibc version 2.20, _SVID_SOURCE is deprecated, see
'man 7 feature_test_macros'. To be able to compile this code without compiler
warnings in new and old glibc versions, both _DEFAULT_SOURCE and _SVID_SOURCE
must be defined.

vpi/sys_scanf.c

@@ -20,6 +20,7 @@
 /* round() is ISO C99 from math.h. This define should enable it. */
 # define _ISOC99_SOURCE 1
 # define _SVID_SOURCE 1
+# define _DEFAULT_SOURCE 1
 
 # include  "sys_priv.h"
 # include  <ctype.h>