dnl Set the appropriate architecture define
case "$host" in
-i?86-*) AC_DEFINE(__i386__);;
-alpha*-*) AC_DEFINE(__alpha__);;
-sparc-*) AC_DEFINE(__sparc__);;
-ppc-*|powerpc-*) AC_DEFINE(__ppc__);;
-ia64-*) AC_DEFINE(__ia64__);;
+i?86-*) AC_DEFINE(__i386__, 1, [Using i386 architecture]);;
+alpha*-*) AC_DEFINE(__alpha__, 1, [Using Alpha architecture]);;
+sparc-*) AC_DEFINE(__sparc__, 1, [Using SPARC architecture]);;
+ppc-*|powerpc-*) AC_DEFINE(__ppc__, 1, [Using PowerPC architecture]);;
+ia64-*) AC_DEFINE(__ia64__, 1, [Using IA-64 architecture]);;
*) echo "$host is not currently supported by ac3dec"; exit 1;;
esac