Add Convert-to-BSD-Makefiles-On-The-Fly system

Note 1: Only needed for BSD/OS.
Note 2: Invent better heuristic (timestamp checks for build/*.mk).
Note 3: Conversion is currently one-way
Note 4: Don't package on BSD/OS.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86284 13f79535-47bb-0310-9956-ffa450edef68