The determination of the name of the posix module's initialization function (at Modules/posixmodule.c:12055)  is currently dependent on the compiler being used.  For MSVC, Watcom, or Borland, the name is defined as "PyInit_nt."  However, both Open Watcom and Borland have shipped compilers for GNU/Linux (and other platforms), making determining the posix module initialization function based on compiler incorrect.

Most other places in Modules/posixmodule.c correctly use the "MS_WINDOWS" preprocessor definition to determine if Windows routines should be used.  Naming the intialization function for the posix module should be dependent on this as well rather than compiler identifiers.  

Linking the interpreter natively with Open Watcom fails under GNU/Linux due to "PyInit_posix" being undefined.  This occurs because of the reasons described above.  The patch included corrects the issue.