silence automake 1.8.x warnings: underquoted definition of...

git-svn-id: http://svn.xiph.org/trunk/ao@8362 0101bb08-14d6-0310-b084-bc0e0c8e3800

ao.m4

@@ -6,7 +6,7 @@
 dnl XIPH_PATH_AO([ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]])
 dnl Test for libao, and define AO_CFLAGS and AO_LIBS
 dnl
-AC_DEFUN(XIPH_PATH_AO,
+AC_DEFUN([XIPH_PATH_AO],
 [dnl 
 dnl Get the cflags and libraries
 dnl