FIX: some compiler problems caused by PM3 master commit 4197a3f6ff for Kali users.

discussed about in isssue ref: https://github.com/Proxmark/proxmark3/issues/218

*untested on icemanfork*

client/whereami.c

@@ -160,7 +160,7 @@ int WAI_PREFIX(getModulePath)(char* out, int capacity, int* dirname_length)
 */
 
 #elif defined(__linux__)
-
+#define _DEFAULT_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>