Change so that the client library config can be accessed using the name
mariadb.pc (or libmariadb.pc).
Rename old mariadb.pc to mariadb-embedded-server.pc to better indicate
that the config is for the daemon build, not client.
Also keep/include names with 'lib' as symlinks, as it aligns with how most
of *.pc files are named in general.
In downstream Debian we already ship the libmariadb.pc as mariadb.pc:
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After this change we would have for the files:
- mariadb.pc for client (with libmariadb.pc as symlink)
- mariadb-embedded-sever.pc for server (with libmariadbd.pc as symlink)
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