more fixes for autoconf 2.50:

more fixes for autoconf 2.50:
ac-2.50 does not use config.cache by default so we cannot use it
to pass arguments to subdirs configure scripts. Instead, we now
export some shell variables to make sure they are part of subdir
configure script's environment

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@10556 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775