Solaris build fixes; don't fail on missing .h files within

  a VPATH build, and don't test trees with -d (simply -f the
  expected files) in case a tree such as srclib/apr is actually
  a symlink rather than a true directory in ./buildconf.

Reviewed by: wrowe, rpluem, colm
Backports: 374821  



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.0.x@374909 13f79535-47bb-0310-9956-ffa450edef68