meson: include the library symbol version list in link_depends

meson: include the library symbol version list in link_depends

This is pretty ugly, because I don't know how to use a single
definition for two purposes:
- --version-script needs a path relative to the build root
- link_depends needs a path relative to source root
Also, link_depends does not accept files() output
[https://github.com/mesonbuild/meson/issues/1172], and I don't see a way to go
from files() output to a string path that can be used to craft the -Wl arg.

Ideally, a single files() result could be used in both places.
I'm leaving this as a separate commit for now.