bison: add autoconf as build dependency

Building Bison 3.3.2 now requires autoconf.

component/bison/buildout.cfg

 [buildout]
 extends =
+  ../autoconf/buildout.cfg
   ../automake/buildout.cfg
   ../m4/buildout.cfg
   ../perl/buildout.cfg
@@ -14,7 +15,7 @@ url = http://ftp.gnu.org/gnu/bison/bison-3.3.2.tar.xz
 md5sum = c9b552dee234b2f6b66e56b27e5234c9
 environment =
   M4=${m4:location}/bin/m4
-  PATH=${automake:location}/bin:${perl:location}/bin:${xz-utils:location}/bin:%(PATH)s
+  PATH=${autoconf:location}/bin:${automake:location}/bin:${perl:location}/bin:${xz-utils:location}/bin:%(PATH)s
 patch-options = -p1
 patches =
   ${:_profile_base_location_}/01_inhibit_example_generation#ee2df22601a56d738939fa760f9dc19b