This only applies when os.name == 'posix'.

Running an un-installed build of Python with the -S
option causes the directory containing the standard
dynamically-built modules not to be placed on sys.path.

The build/lib.<platform>-<version>/ directory
containing those modules is added to sys.path by
site.py rather than getpath.c, even though those
modules are needed.  This includes many modules on most
Unix systems:

array          dbm            math      regex     termios
audioop        dl             md5       resource  _testcapi
binascii       errno          mmap      rgbimg    time
bsddb          fcntl          mpz       rotor     timing
cmath          fpectl         nis       select    _tkinter
_codecs        gdbm           operator  sha      
unicodedata
cPickle        grp            parser    _socket   _weakref
crypt          _hotshot       pcre      _ssl     
xreadlines
cStringIO      _hotshot       pwd       strop     zlib
_curses_panel  linuxaudiodev  pyexpat   struct
_curses        _locale        readline  syslog

Perhaps the best way to fix this is to add the
equivalent code to getpath.c.  The relevant stanza in
site.py is headed by a comment saying "especially for
Guido".