include sys/file.h for LOCK_EX

Fixes
| ../git/src/basic/user-util.c:708:30: error: use of undeclared identifier 'LOCK_EX'; did you mean 'LOCK_BSD'?
|   708 |         r = unposix_lock(fd, LOCK_EX);
|       |                              ^~~~~~~
|       |                              LOCK_BSD

Signed-off-by: Khem Raj <raj.khem@gmail.com>

src/basic/user-util.c

@@ -6,6 +6,7 @@
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <sys/file.h>
 #include <sys/stat.h>
 #include <unistd.h>
 #include <utmp.h>