When attempting to link in mcrypt capability, numerous
warnings and errors are given. The mcrypt
package being used is 2.5.4, while the libmcrypt
version is 2.4.4 (latest available)

It appears as if an interface change has been made -
the compile complains about register_long_constant
passing in strings instead of integers.

The configure line in php was

 ./configure --with-apache=../apache_1.3.9 --enable-debug=no
           --prefix=/usr/local/apache
            --with-zlib --with-imap --with-mcrypt
           --with-mhash --with-pgsql --with-gd

After fixing a bunch of undefined variables (e.g. BLOWFISH_448
doesn't exist - changed it to BLOWFISH, and so on, in the
ext/mcrypt/mcrypt.c file, the compile then complains about the
type definition mismatch as described above.