configure.ac: use AC_PROG_MKDIR_P

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=45057
diff --git a/configure.ac b/configure.ac
index a68a90f..9599568 100644
--- a/configure.ac
+++ b/configure.ac
@@ -47,6 +47,7 @@
 AC_CHECK_PROGS([MAKE], [gmake make])
 AC_CHECK_PROGS([PYTHON2], [python2 python])
 AC_PROG_SED
+AC_PROG_MKDIR_P
 AC_PATH_PROG([MKDEP], [makedepend])
 
 if test "x$MKDEP" = "x"; then