Allow compilation with mariadb-connector-c

[bibstha]

In the original PR where we introduce session_tracking on mysql2 gem, we used the constant CLIENT_SESSION_TRACK.

I found out that mariadb-connector-c uses CLIENT_SESSION_TRACKING instead and therefore the mysql2 gem wouldn't work.
mariadb also defines an enum value SESSION_TRACK_TRANSACTION_TYPE instead of mysql's SESSION_TRACK_TRANSACTION_STATE.

In our codebase, we use mariadb-connector-c on dev while mysql-connector-c on ci and production. To make it work on all, we need this patch.

[bibstha]

Similar hacks are used in few lines above in

mysql2/ext/mysql2/client.c

Lines 52 to 55 in 360e63d

	#if defined(MARIADB_CLIENT_VERSION_STR)
	#define MYSQL_LINK_VERSION MARIADB_CLIENT_VERSION_STR
	#elif defined(LIBMYSQL_VERSION)
	#define MYSQL_LINK_VERSION LIBMYSQL_VERSION

[insom]

🍴-- Hooray for copying a feature but changing it very slightly from the original 😁. I am also curious why we use a different connector in Railgun than we do for CI and production, but that seems like a bigger yak than this 5 line code change.

[bibstha]

🍴-- Hooray for copying a feature but changing it very slightly from the original 😁. I am also curious why we use a different connector in Railgun than we do for CI and production, but that seems like a bigger yak than this 5 line code change.

We recently moved to nix on dev. And turns out in nix, all gems and their dependencies (in our case mysql2 and it's dependency on libmysqlclient) is defined deep in nix config. We can ofcourse override that, however if we are to get the session tracker patch on the mainline mysql2 gem, we need this patch so it works for everyone. Therefore fixing it here.