$NetBSD$

replace obsolete macro.

--- configure.ac.orig	2013-06-14 13:22:11.000000000 +0000
+++ configure.ac	2013-06-14 13:22:29.000000000 +0000
@@ -128,7 +128,7 @@
 #
 # Finish up
 #
-AM_CONFIG_HEADER(pre_config.h)
+AC_CONFIG_HEADERS(pre_config.h)
 AC_CONFIG_FILES([Makefile
 		   src/Makefile
 		   pidgin-festival.spec
