Each extension has its own configuration and installation section, and these sections don't really follow a standard. We need a standard.
The main issue is Windows versus Unix. Currently this is done in many ways so it's rather confusing.
For details, see: http://markmail.org/message/c7hz3yycg4mvyje5
Whether or not an extension is in PECL is another issue, as is worrying about if it moved to or from PHP core.
Essentially this task involves three steps.