Observed once in about two dozen builds on the bots:

make[6]: *** No rule to make target '/build/lede-snapshots/arm_cortex-a7_neon-vfpv4/build/sdk/staging_dir/target-arm_cortex-a7+neon-vfpv4_musl_eabi/usr/lib/libevent.so', needed by 'tests/async_queries'.  Stop.

Address this by adding libevent2 to PKG_BUILD_DEPENDS.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>

MariaDB is a drop-in replacement for MySQL. This commit adds a current
and stable version of MariaDB to the tree.

Quite a few ideas/patches were copied from Alpine Linux, Busybox Buildroot
and Debian.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>