Please refer to README.SELF-CONTAINED-EXTENSIONS from the original source distribution

—-from the readme file—-

Just to show you how easy it is to create a self-contained
extension, we will convert an embedded extension into a
self-contained one. Install PHP and execute the following
commands.

$ mkdir /tmp/newext
$ cd /tmp/newext

You now have an empty directory. We will copy the files from
the mysql extension:

$ cp -rp php-4.0.X/ext/mysql/* .

It is time to finish the module. Run:

$ phpize

You can now ship the contents of the directory – the extension
can live completely on its own.

The user instructions boil down to

$ ./configure \
[--with-php-config=/path/to/php-config] \
[--with-mysql=MYSQL-DIR]
$ make install

The MySQL module will either use the embedded MySQL client
library or the MySQL installation in MYSQL-DIR.