pypy3: build cffi extensions in lib_pypy

Fixes a problem reported on IRC where these modules can't be imported by
a different user than the user that installed Homebrew because building
the cffi extensions writes files to the Cellar. Pypy's packaging script
normally generates these but it isn't invoked by Homebrew.

Closes #33813.
pypy: build cffi extensions in lib_pypy

Fixes a problem reported on IRC where these modules can't be imported by
a different user than the user that installed Homebrew because building
the cffi extensions writes files to the Cellar. Pypy's packaging script
normally generates these but it's not invoked by Homebrew.

Closes #33725.