attaching an updated patch. besides renaming of the platform directory, the following changes are made:

 - it makes the name of the internal _sysconfigdata module dependent
   on the abiflags
 - it moves the _sysconfigdata module into the platform directory.
   This address as well #22724, it should address #18083 as well,
   provided that some multiarch tuples for solaris are defined.
 - it fixes regeneration of the Python modules from C headers for
   cross builds.
 - it introduces a sys.implementation._multiarch attribute to construct
   the name of the platform directory without having the
   _sysconfigdata module available (which now is located in the platform
   dir)

One outstanding issue probably is the generation of the platform directory in the source tree, not in the build tree (but this is existing behaviour).

This should address #12619 (this patch probably needs an update),