Add experimental cmake-based build system for Windows.

(Support for both trunk and 2.4.x has been removed for this first commit
to the 2.4.x branch.)

Thanks tdonovan for sharing your earlier version!  A lot
of good stuff is from Tom; a lot of bad stuff is from me.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1541921 13f79535-47bb-0310-9956-ffa450edef68