./configure --with-modules=mod_sql:mod_sql_mysql --with-includes=/usr/local/mysql/current/include/ --with-libraries=/usr/local/mysql/current/lib

Quote

mod_sql_mysql.c: In function `cmd_select':
mod_sql_mysql.c:804: warning: implicit declaration of function `mysql_real_query'
mod_sql_mysql.c:804: dereferencing pointer to incomplete type
mod_sql_mysql.c: In function `cmd_insert':
mod_sql_mysql.c:918: dereferencing pointer to incomplete type
mod_sql_mysql.c: In function `cmd_update':
mod_sql_mysql.c:1017: dereferencing pointer to incomplete type
mod_sql_mysql.c: In function `cmd_query':
mod_sql_mysql.c:1133: dereferencing pointer to incomplete type
mod_sql_mysql.c:1148: warning: implicit declaration of function `mysql_field_count'
mod_sql_mysql.c:1148: dereferencing pointer to incomplete type
mod_sql_mysql.c: In function `cmd_escapestring':
mod_sql_mysql.c:1228: warning: implicit declaration of function `mysql_escape_string'
mod_sql_mysql.c: In function `cmd_checkauth':
mod_sql_mysql.c:1295: warning: implicit declaration of function `make_scrambled_password'
make[1]: *** [mod_sql_mysql.o] Error 1
make[1]: Leaving directory `/backup/install/proftpd-1.2.9/modules'