Blender Git Loki

Fix OSL shaders building with some versions of that lib.

This must have happened months ago, but as I did not `make clean` any build folder since then,
so only noted that today.

Issue is same as dirty patch we have to apply to ODL sources before building it in install_deps.sh - for
some mysterious reason, it has become impossible to compoile .osl files into .oso ones without
giving explicit output file name (otherwise it just produces `.oso` file - utterly stupid and useless).

We could probably fix that in own OSL source, but think being explicit here does not hurt anyway, so...
Let's go the easy way.