Currently there is only one platform directory for all linux architectures, there are two reasons to have a separate directory for each architecture:

 - the contents of the files in this directory differ
   (most prominent case are the RTLD_* constants on various
   architectures).

 - The _sysconfigdata.py module is installed in the platdir.
   A cross build of the extensions in the standard library
   is done by running the python interpreter for the build
   machine with the platdir for the host machine.  This
   currently works for cross builds targeting a different
   os, but not cross building from one linux architecture
   to another.

This would then remove Lib/plat-linux and introduce some Lib/plat-$(PLATFORM_TRIPLET) directories.