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sysconfig is looking for the source dir when 
 sysconfig.get_config_var('srcdir')
is called.
And this is done like this:
if sys.executable:
 _PROJECT_BASE = os.path.dirname(_safe_realpath(sys.executable))
else:
 # sys.executable can be empty if argv[0] has been changed and Python is
 # unable to retrieve the real program name
 _PROJECT_BASE = _safe_realpath(os.getcwd())
Because sys.executable (argv[0] in fact) is not filled when you call multiprocess vvia the -j option.
So yeah, this has to do with sys.executable