Darwin: include <libgen.h> for basename(3).

Test: treehugger
Change-Id: I11858430f13cbb22895c9dd0befb8054308efb19
diff --git a/libziparchive/unzip.cpp b/libziparchive/unzip.cpp
index 7332b41..e4839b4 100644
--- a/libziparchive/unzip.cpp
+++ b/libziparchive/unzip.cpp
@@ -19,6 +19,7 @@
 #include <fnmatch.h>
 #include <getopt.h>
 #include <inttypes.h>
+#include <libgen.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>