clang doesn't support --version-script so falls back on linking with –-export-symbols-regex "^mongoc_".

Unfortunately, we haven't been entirely religious about our function naming conventions, and have plenty of private functions that start with mongoc_ rather then _mongoc.

This leads to functions like mongoc_set_new, mongoc_stream_tls_openssl_bio_meth_new, mongoc_topology_scanner_add and plenty more are part of our "public abi" when using clang.

We need to fix this, likely by removing the use of --version-script so we can have just one implementation of this, rather then multiple