include libgen.h for basename(3)

Index: tests/util/piglit-util.c
--- tests/util/piglit-util.c.orig
+++ tests/util/piglit-util.c
@@ -41,6 +41,7 @@
 #include <errno.h>
 #include <inttypes.h>
 #include <time.h>
+#include <libgen.h>
 
 #if defined(PIGLIT_HAS_POSIX_CLOCK_MONOTONIC) && defined(PIGLIT_HAS_POSIX_TIMER_NOTIFY_THREAD)
 #include <pthread.h>