clang: possible better compilation with musl c

Try to help resolving reported compilation problem with
clang & musl C.
https://github.com/lvmteam/lvm2/issues/61

libdaemon/server/daemon-server.c

@@ -18,6 +18,7 @@
 
 #include <dlfcn.h>
 #include <errno.h>
+#include <fcntl.h> /* help musl C */
 #include <pthread.h>
 #include <sys/file.h>
 #include <sys/stat.h>