configure: new --dynamic-libengines build option

configure: new --dynamic-libengines build option

When enabled, some of the more dependency-heavy internal engines are
converted to "plugin" engines, i.e. they are built into separate object
files and are loaded by fio on demand.
This helps downstream distros package these engines separately and not
force a long list of package dependencies from the base fio package.

Signed-off-by: Yigal Korman <ykorman@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>