Compile qemu-nbd also on OpenBSD and Solaris

basename() needs #include <libgen.h>.

No prototype for daemon() is available on Solaris, but link
succeeds.

Signed-off-by: Blue Swirl <[email protected]>
diff --git a/qemu-nbd.c b/qemu-nbd.c
index 6cdb834..91ea014 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -30,6 +30,7 @@
 #include <netinet/tcp.h>
 #include <arpa/inet.h>
 #include <signal.h>
+#include <libgen.h>
 
 #define SOCKET_PATH    "/var/lock/qemu-nbd-%s"