I have confirmed this on 2 server both running red hat 7.2 it will also not compile in the current cvs version 

compile string
LIBS="-lmcrypt -lltdl" ./configure  --with-mysql=/usr  --with-curl  --with-apache=../apache_1.3.23/  --enable-wddx  --enable-dbx  --enable-track-vars  --with-mcrypt  --with-mhash  --with-xml  --with-OpenSSL=/usr  --enable-bcmath  --enable-calendar  --enable-ftp  --enable-sockets  --with-jpeg-dir=/usr/lib  --with-png-dir=/usr/lib  --with-tiff-dir=/usr/lib --with-vpopmail

Output from make
Making all in vpopmail
make[2]: Entering directory `/usr/src/httpd/php-4.1.2/ext/vpopmail'
make[3]: Entering directory `/usr/src/httpd/php-4.1.2/ext/vpopmail'
gcc -I. -I/usr/src/httpd/php-4.1.2/ext/vpopmail -I/usr/src/httpd/php-4.1.2/main -I/usr/src/httpd/php-4.1.2 -I/usr/src/httpd/apache_1.3.23/src/include -I/usr/src/httpd/apache_1.3.23/src/os/unix -I/usr/src/httpd/php-4.1.2/Zend -I/usr/local/include -I/usr/include/mysql -I/home/vpopmail/include -I/usr/src/httpd/php-4.1.2/ext/xml/expat  -I/usr/src/httpd/php-4.1.2/TSRM -g -O2  -c php_vpopmail.c && touch php_vpopmail.lo
php_vpopmail.c:925:8: warning: extra tokens at end of #endif directive
php_vpopmail.c: In function `zif_vpopmail_add_alias_domain':
php_vpopmail.c:288: warning: passing arg 3 of `add_domain_assign' makes pointer from integer without a cast
php_vpopmail.c:288: too few arguments to function `add_domain_assign'
make[3]: *** [php_vpopmail.lo] Error 1
make[3]: Leaving directory `/usr/src/httpd/php-4.1.2/ext/vpopmail'
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory `/usr/src/httpd/php-4.1.2/ext/vpopmail'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/usr/src/httpd/php-4.1.2/ext'
make: *** [all-recursive] Error 1