Feature request: Optionally exclude large buffers from core dumps

As the size of core dump files by default mostly equals the process size producing core dumps can become an issue on systems with memory buffers, esp. large innodb_buffer_pool_size.

There needs to be enough file system space to store such large core dumps, and with multi gigabyte files it also takes a non-trivial amount of time to write these, so delaying process restart quite a bit.

And then there's also a security aspect to it: as the core dump contains the complete innodb buffer pool it contains a substantial amount, or even all, of the actual user data in the database.

At the same time actual buffer contents are rarely needed when doing a post mortem analysis (usually we only need stack frames and a few pieces of local data).

So I'm proposing a server option to exclude certain buffers from core dumps by marking them as DONOTDUMP with the madvise() system call.