How to make OCI8 uses 9iR2client libraries on Linux?

Question

I need to connect to an Oracle 8i server, but oci8 does not support it by default.

The php documentation says as following:

Note:

If OCI8 uses 9iR2 client libraries, then PHP can connect to Oracle Database 8i, 9iR2, 10g or 11g. If OCI8 uses 10gR2 client libraries, the database can be 9iR2, 10g, 11g or 12c. If OCI8 uses 11g client libraries, the database can be 9iR2, 10g, 11g or 12c. If OCI8 uses 12c client libraries, the database can be 10gR2, 11g or 12c.

How can I setup OCI8 to use 9iR2 client libraries?

My current environment is:

I'm on a ubuntu server,
Oracle 8i version 8.1.7.4.0
I have already installed instantclient libraries(I'm able to connect to oracle 10i and above)
I'm using instantclient version 12.1... Also tried with instantclient version 10.2

Could someone help me figuring out what the problem might be and how to solve it? Any help is really appreciated.

Thank you