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- [x] Add new / update outdated documentation

_osx_support.py
_aix_support.py
curses
dbm
ensurepip
idlelib
lib2to3
tkinter
turtle.py
turtledemo
venv
distutils/command/wininst-*.exe
webbrowser.py
sqlite3
ssl.py
lzma.py
_pydecimal.py
pydoc_data

_osx_support.py
_aix_support.py
curses
dbm
ensurepip
idlelib
lib2to3
tkinter
turtle.py
turtledemo
venv
distutils/command/wininst-*.exe
webbrowser.py
sqlite3
ssl.py
lzma.py
_pydecimal.py
pydoc_data
