Fix a VPATH build issue - our command lines can sometimes hit the wall
  against the shell's max command line length.  We had a number of needless
  paths included in VPATH builds; this change will spare us from -I'ncluding
  the module paths with no .h files.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@99861 13f79535-47bb-0310-9956-ffa450edef68