When compiling mod_ruby under Fedora Core 5, and thus Apache 2.2, configure.rb assumes an incorrect path for the apr* files, and make kicked out the following errors:
# make
In file included from /usr/include/httpd/httpd.h:43,
from mod_ruby.h:49,
from mod_ruby.c:33:
/usr/include/httpd/ap_config.h:25:17: error: apr.h: No such file or directory
/usr/include/httpd/ap_config.h:26:23: error: apr_hooks.h: No such file or directory
/usr/include/httpd/ap_config.h:27:32: error: apr_optional_hooks.h: No such file or directory
…
The [...]