build-sys: Link with -ldl for rust build
build-sys: Link with -ldl for rust build

I didn't dive into this too much, it looks like something in rust changed that
broke our build. Probably libstd gained a dependency on `-ldl` or so, and that's
handled by cargo? Anyways linking against it isn't going to hurt.

Closes: #1391
Approved by: smcv

GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree,GNOME/ostree