pg

How to compile sqlite3, mysql and postgres driver for Rails 3.X on Mac OS X Leopard?

Is there a reason why all sqlite3, mysql, postgres driver compiles on Mac OS X Leopard when it is Rails 2.3.8, but can't compile when it is Rails 3.x? Theoretically, isn't it just some compile flags to make them work? (They all compile on Snow Leopard with the latest Xcode, but can't compile with Leopard with a slightly older Xcode... ...