Use dirname (3) instead of our own code

Related: rpm-software-management#2928

rpmio/macro.c

@@ -6,6 +6,7 @@
 #include <stdarg.h>
 #include <pthread.h>
 #include <errno.h>
+#include <libgen.h>
 #ifdef HAVE_SCHED_GETAFFINITY
 #include <sched.h>
 #endif
@@ -1306,23 +1307,9 @@ static void doFoo(rpmMacroBuf mb, rpmMacroEntry me, ARGV_t argv, size_t *parsed)
 	    b++;
     } else if (rstreq("dirname", me->name)) {
 	buf = xstrdup(argv[1]);
-	if (!strcmp(buf, "")) {
-	    buf = rstrcat(&buf, ".");
-	} else {
-	    /* strip trailing / */
-	    size_t l = strlen(buf);
-	    if (l > 1 && buf[l-1] == '/')
-		buf[l-1] = '\0';
-	    if ((b = strrchr(buf, '/')) != NULL)
-		if (b == buf)
-		    /* keep root dir */
-		    buf[1] = '\0';
-		else
-		    *b = '\0';
-	    else
-		strcpy(buf, ".");
-	}
-	b = buf;
+	b = xstrdup(dirname(buf));
+	free(buf);
+	buf = b;
     } else if (rstreq("shrink", me->name)) {
 	/*
 	 * shrink body by removing all leading and trailing whitespaces and