util: Use strrchr instead of GNU basename

The GNU basename behavior can be replicated easily with strrchr,
so just use that, since some platforms (like musl libc) don't have
GNU basename.

Author: michaelforney

src/util.c

@@ -2,6 +2,7 @@
 
 #include <ctype.h>
 #include <fcntl.h>
+#include <libgen.h>
 #include <poll.h>
 #include <stdarg.h>
 #include <sys/stat.h>
@@ -15,12 +16,6 @@
 #  include <sys/random.h>
 #endif
 
-/* When we include libgen.h because we need dirname() we immediately
- * undefine basename() since libgen.h defines it as a macro to the
- * POSIX version which is really broken. We prefer GNU basename(). */
-#include <libgen.h>
-#undef basename
-
 #include "def.h"
 #include "time-util.h"
 #include "util.h"
@@ -482,7 +477,8 @@ int tempfn_random(const char *p, char **ret) {
          *         /foo/bar/.#waldobaa2a261115984a9
          */
 
-        fn = basename(p);
+        fn = strrchr(p, '/');
+        fn = fn ? fn + 1 : p;
         if (!filename_is_valid(fn))
                 return -EINVAL;