## Specify DESTDIR on command line

`meson install` command now has a `--destdir` argument that overrides `DESTDIR`
from environment.

## Skip install scripts if DESTDIR is set

`meson.add_install_script()` now has `skip_if_destdir` keyword argument. If set
to `true` the script won't be run if `DESTDIR` is set during installation. This is
useful in the case the script updates system wide caches, or performs other tasks
that are only needed when copying files into final destination.