supercollider 1:3.7.0~repack-2: how to deactivate oscpack

[Dan S]

Hi Felipe and all,

Thanks for tweaking and uploading 1:3.7.0~repack-2 of supercollider.
Now we're down to one single build error appearing on a few archs...

The error is caused by attempting to compile the bundled "oscpack".
However, the problem shouldn't be there, because on those platforms
supernova is disabled, and it's only supernova that uses oscpack.

In the file `external_libraries/CMakeLists.txt` the oscpack lib is set
as EXCLUDE_FROM_ALL which is *supposed* to mean that it'll not get
built if none of its dependents are getting built.

There must be some CMake tweak needed, but it's not clear to me why
EXCLUDE_FROM_ALL doesn't suffice. Insights welcome. Otherwise we may
need to just "if()" the thing away on those archs.

Cheers
Dan