http://bugs.gentoo.org/326939
http://repos.archlinux.org/wsvn/packages/pkg-config/trunk/autoconf-2.66.patch

--- pkg.m4
+++ pkg.m4
@@ -135,7 +135,7 @@
 Consider adjusting the PKG_CONFIG_PATH environment variable if you
 installed software in a non-standard prefix.
 
-_PKG_TEXT])dnl
+_PKG_TEXT])[]dnl
         ])
 elif test $pkg_failed = untried; then
      	AC_MSG_RESULT([no])