libs : rename libcommon -> libllama-common (#21936)
* cmake : allow libcommon to be shared
* cmake : rename libcommon to libllama-common
* cont : set -fPIC for httplib
* cont : export all symbols
* cont : fix build_info exports
* libs : add libllama-common-base
* log : add common_log_get_verbosity_thold()
