CGI or php-based packages often don't care about the specific webserver used, but they do need something. I suggest virtual/httpd default to net-www/apache, but all of the webservers should provide virtual/httpd. Note: since it's possible to have more than one webserver running, it's important that the various servers do _not_ have a "!virtual/httpd" dependency!
wrangler
*** This bug has been marked as a duplicate of 11007 ***