18c install missing symlinks for Oracle 12 shared libraries?

We're trying to use/test Pro*C code compiled and dynamically linked with Oracle 12.1, in an Oracle 18c environment on Linux x64. The binaries all fail at runtime with

things like libclntshcore.so.12.1 not found by the loader.

On an 18c environment:

cd $ORACLE_HOME/lib

ls -l *clnt*

lrwxrwxrwx. 1 oracle dba        21 Nov 21 11:23 libclntshcore.so -> libclntshcore.so.18.1

-rwxr-xr-x. 1 oracle dba   8349480 Nov 21 11:23 libclntshcore.so.18.1

lrwxrwxrwx. 1 oracle dba        17 Nov 21 11:23 libclntsh.so -> libclntsh.so.18.1

lrwxrwxrwx. 1 oracle dba        12 Nov 21 11:22 libclntsh.so.10.1 -> libclntsh.so

lrwxrwxrwx. 1 oracle dba        12 Nov 21 11:22 libclntsh.so.11.1 -> libclntsh.so

-rwxr-xr-x. 1 oracle dba  77800560 Nov 21 11:23 libclntsh.so.18.1

You can see there's only one actual binary for libclntsh and symlinks for 10.1 and 11.1 pointing to it, but nothing for 12.1