Add comments clarifying what the three non-FreeBSD platforms using
G_CREDENTIALS_USE_FREEBSD_CMSGCRED are.
#define G_CREDENTIALS_SOCKET_GET_CREDENTIALS_SUPPORTED 1
#define G_CREDENTIALS_SPOOFING_SUPPORTED 1
-#elif defined(__FreeBSD__) || defined(__FreeBSD_kernel__) || defined(__GNU__) || defined(__DragonFly__)
+#elif defined(__FreeBSD__) || \
+ defined(__FreeBSD_kernel__) /* Debian GNU/kFreeBSD */ || \
+ defined(__GNU__) /* GNU Hurd */ || \
+ defined(__DragonFly__) /* DragonFly BSD */
#define G_CREDENTIALS_SUPPORTED 1
#define G_CREDENTIALS_USE_FREEBSD_CMSGCRED 1
#define G_CREDENTIALS_NATIVE_TYPE G_CREDENTIALS_TYPE_FREEBSD_CMSGCRED