Defaults to /usr/lib* might be harmful

[bfloch]

Here is the case:
If you provide custom library paths but some of the libraries are not given /usr/lib is being added as default.
However this default might mess up the linking for all other libraries if the system happens to have the same libraries.

The concrete use-case was where alembic would fail to link against hdf5 in the tests because our alembic was linked against a newer hdf.
However since a different path was not specified it defaulted to /usr/lib. The order of these variable is random and in our case the system library was being linked (and failed) before our provided hdf5 path.

This was 8.4 but I still see /usr/lib as defaults in dev.
I would suggest not to default to /usr/lib* but instead leave the path empty.
ld always picks up /usr/lib as last resort so no action is necessary.

Cheers,
Blazej

[johnhaddon]

This was fixed by 69ff112 - closing.