bpo-28552: Fix distutils.sysconfig for empty sys.executable (GH-12875) (GH-12948)

bpo-28552: Fix distutils.sysconfig for empty sys.executable (GH-12875) (GH-12948)

bpo-28552, bpo-7774: Fix distutils.sysconfig if sys.executable is
None or an empty string: use os.getcwd() to initialize project_base.

Fix also the distutils build command: don't use sys.executable if
it's evaluated as false (None or empty string).
(cherry picked from commit 0ef8c157e9195df0115c54ba875a5efb92ac22fb)

Co-authored-by: Victor Stinner <vstinner@redhat.com>