Overall UNIX build system improvements:

* Makefile header is now completely dynamic
* Absolute paths everywhere
  (fixes Tru64 support)
* Get rid of LTLIBRARY_SHARED_NAME rule in library.mk
  (fixes Irix support, untested)
* VPATH does not contain variables anymore
  (fixes UnixWare support)
* Remove inclusion of program.mk in support/Makefile.in
  (PROGRAM_NAME is empty => breaks Irix and others)
* Call REENTRANCY_FLAGS earlier, so that flags are passed to header checks
  (might fix OpenBSD pthread.h-detection, untested)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@85102 13f79535-47bb-0310-9956-ffa450edef68