bcachefs-tools: Use basename(3) from <libgen.h>

Although glibc also provides basename(3) from <string.h>, this is
non-standard whereas it is available from <libgen.h> portably.

Signed-off-by: Chris Webb <chris@arachsys.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

libbcachefs.c

@@ -2,6 +2,7 @@
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <libgen.h>
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>