As described in https://github.com/MariaDB/server/pull/3531 I suggest adding `noexcept` annotations to various methods throughout the MariaDB code base, starting with the InnoDB locking code.

MariaDB is compiled with C++ exceptions enabled, and that disallows some optimizations (e.g. the stack must always be unwinding-safe).  By adding `noexcept` to functions that are guaranteed to never throw, some of these optimizations can be regained.  Low-level locking functions that are called often are a good candidate for this.