Inigo Martínez authored Dec 14, 2017 and Thomas Haller committed Dec 14, 2017

generate-settings-docs.py script uses the `LD_LIBRARY_PATH` to
prepend directories to the library search path, which is useful to
load a just built libnm shared library, when generating the
`nm-settings-docs.xml` and `nm-property-docs.xml` files.

However, this is a problem for meson, which is not able to set
environment variables when executing the script.

This patch adds a new optional parameter, `-l` or `--lib-path` that
can be used to pass different paths to be prepended without using
the `LD_LIBRARY_PATH` environment, which can still be used.

[thaller@redhat.com: fix script to handle None lib_path argument]

https://mail.gnome.org/archives/networkmanager-list/2017-December/msg00044.html