Download latest IBM_DB2 extension source code from PECL. Extract it and put it in standard location (PECL directory).
Download IBM Data Server Driver Package from the link provided in Dependencies section. Install this package on the server (say, the location will be C:\SQLLIB).
Once the installation is done, next step is to setup the environment. Open VC command prompt and set few environment variables. Following are the command to set these variables:
> set LIB="C:\SQLLIB\lib";%LIB% > set INCLUDE="C:\SQLLIB\include";%INCLUDE% > set PATH="C:\SQLLIB\bin";%PATH%
After this step, run standard steps to build PHP. The flag to include IBM_DB2 extension is –with-ibm_db2, and it should point to SQLLIB directory. So, in current case, the flag will be like:
> configure --with-ibm_db2="C:\SQLLIB",shared