Add missing <fcntl.h> includes

These are required due to the O_* macro usage, but have passed
undetected on glibc-based systems due to implicit inclusions.

Signed-off-by: Guillem Jover <guillem@hadrons.org>

src/flopen.c

@@ -32,6 +32,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/stat.h>
 
 #include <errno.h>
+#include <fcntl.h>
 #include <stdarg.h>
 #include <unistd.h>
 #include <libutil.h>