Debian/Ubuntu:
  libapr1-dev /usr/include/apr-1.0
  apache2-dev /usr/include/apache2

Fedora/RHEL:
  apr-devel   /usr/include/apr-1
  httpd-devel /usr/include/httpd

FreeBSD:
  apr         /usr/local/include/apr-1
  apache24    /usr/local/include/apache24