use RTLD_LOCAL so that symbols are *only* exposed via dlsym
without this all symbols exported by the libs are available for symbol
resolution, resulting in different lib versions potentially resolving
*each other's* symbols, causing incredibly cursed behavior such as
https://gist.github.com/apage43/085c1ff69f6dd05387793ebc301840f6
Major change to the backend that allows for pluggable versions of llama.cpp/ggml. This was squashed merged from dlopen_backend_5 where the history is preserved.
