Client lib compatibility v. 7.2, 7.3 and 7.4

Hi,
I know that 7.2, 7.3, and 7.4 are not compatible. But I'm wondering if the
client lib (libpq.so) is compatible across those versions.

The thing is, my old database is 7.2. I upgrade my system using Redhat
Enterprise, which shipped with 7.3 and use the client of the PHP-pgsql module
(PHP compiled with --with-pgsql flag). So I assume the PHP use 7.3 client.

For some reason the Redhat version of postgreSQL is weird with its own default
conf, it confuses me. I'm frustrated and decided to compile my own PostgreSQL
downloaded from the website. I'm thinking of going with 7.4, since it's the
latest, but wondering if I need to recompile my PHP install. If the client is
compatible, then I assume I don't have to recompile PHP. Otherwise I'll stick
with 7.3 for now.

Thanks for any info.
Reuben D. Budiardja