Always include buf_madvise_do_dump in binaries.

Hi,

as described in [1], the buf_madvise_do_dump function is added but never called by the server; it is there to be called from a debugger to re-enable full core dump if needed.

[1]: https://github.com/MariaDB/server/pull/364/commits/b600f30786816e33c1706dd36cdabf21034dc781

As described in [2], this function is not present in the Linux generic binaries. This leads to wasted time in debugging.

[2]: https://www.percona.com/community-blog/2018/06/28/nice-feature-in-mariadb-103-no-innodb-buffer-pool-in-coredumps/

As described in [2], if would be better to always have this function in binaries and to behave differently depending if the "no InnoDB Buffer Pool in core dumps" feature is included or not in the binaries. An example of such behavior could be to return a non-zero value when failing with a detailed message in the error logs.

Please consider implementing this for easing the usage of MariaDB.

Thanks in advance,

JFG