Missing includes; required at least for compiling against musl.

diff --git a/gencat/gencat.c.orig b/gencat/gencat.c
index d1a7c31..99be7fa 100644
--- a/gencat/gencat.c.orig
+++ b/gencat/gencat.c
@@ -55,6 +55,7 @@ up-to-date.  Many thanks.
 #endif
 #include <sys/file.h>
 #include <sys/stat.h>
+#include <fcntl.h>
 #include "gencat.h"

 #ifndef L_SET