Thanks for the responses. Since the underlying knob flip is a paid version and we are a SaaS based service provider, this might not align well with our requirement and so wanted to build postgres-10 against FIPS compliant ssl/crypto. The "pg_config" is of of great help in order to understand the build time configure options.
Huh? There is *nothing* in PostgreSQL that is a paid version (there is no such thing, simply), nor in any of our open source packaging.
If you are specifically looking at the Debian or Ubuntu packages, you can find the full packaging information in the salsa repositories at https://salsa.debian.org/postgresql/postgresql. It will have all teh details you need.