Fix warning on Darwin 8.7.0 (OS X 10.4.7) due to the prototype for

sendfile_nonblocking being declared outside ifdefs even though the
function is defined and used only when APR_HAS_SENDFILE



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@425571 13f79535-47bb-0310-9956-ffa450edef68