I recently made a build with a number of options enabled. With my full configure line, the mcrypt library detection would fail ("error: Sorry" after the two version checks)
./configure --with-apxs=/usr/sbin/apxs --with-mysql --with-imap=../imap-2000a/ --with-pdflib --with-bz2 --with-openssl --with-mm --with-pspell --enable-bcmath --with-curl --with-dom --enable-ftp --with-gd --enable-gd-imgstrttf --with-jpeg-dir --with-gettext --with-java --with-ldap --with-mcrypt --with-mhash --with-pgsql --enable-shmop --enable-sockets --with-swf=/home/chris/libswf-0.99/ --enable-sysvsem --enable-sysvshm --with-zlib --enable-inline-optimization --enable-memory-limit --enable-shared
fails. If I did a bare ./configure --with-mcrypt, the library would be detected. I could then re-run the full script, as the mcrypt detection was cached.