So as a fix, I updated dependency to openssl11-devel in rpmspec, and added extra code to CMakeLists.txt to locate openssl11 headers and libs on CentOS. Now, libcouchbase will only build version without SSL only if the user explicitly asks for it with LCB_NO_SSL flag to cmake. Otherwise it will fail if OpenSSL is not found.
The problem was appeared when I updated Jenkins pipeline for Amazon Linux 2 to use OpenSSL 1.1 (to support Capella). So libcouchbase-3.3.0 for amzn2 was built properly. But on CentOS 7 they moved the headers and libraries of OpenSSL 1.1 into extra prefix, so that CentOS 7 can install not just libraries for 1.0 and 1.1 simultaneous, but also the -devel packages (the headers). With "fallback to non-SSL build" behaviour of libcouchbase, it produced build that does not support OpenSSL.
Once patch will be reviewed and merged, I will create tag 3.3.1 and publish new libcouchbase binaries.