BLD Add DISTDIR variable. ### Description

Adds `DISTDIR` env variable that points to the directory where libraries should be copied to when building shared libraries with recipe.

### Checklists

- [x] Add new / update outdated documentation

package:
  name: traits
  version: 6.4.1
  top-level:
    - traits
source:
  sha256: 78bb2ccafd60aff606515aac46de64668a0a81cb5c54c650b9877a841aa9e812
  url: https://files.pythonhosted.org/packages/ca/72/8d08717884ac41811c4cdbd5bce3101a3df64e0a1890aab7b1a1311c1f50/traits-6.4.1.tar.gz
about:
  home: http://docs.enthought.com/traits
  PyPI: https://pypi.org/project/traits
  summary: Observable typed attributes for Python classes
  license: BSD

package:
  name: traits
  version: 6.4.1
  top-level:
    - traits
source:
  sha256: 78bb2ccafd60aff606515aac46de64668a0a81cb5c54c650b9877a841aa9e812
  url: https://files.pythonhosted.org/packages/ca/72/8d08717884ac41811c4cdbd5bce3101a3df64e0a1890aab7b1a1311c1f50/traits-6.4.1.tar.gz
about:
  home: http://docs.enthought.com/traits
  PyPI: https://pypi.org/project/traits
  summary: Observable typed attributes for Python classes
  license: BSD
