plat-$(PLATFORM_TRIPLET).
Rename the config directory (LIBPL) from config-$(LDVERSION) to
config-$(LDVERSION)-$(PLATFORM_TRIPLET).
Install the platform specifc _sysconfigdata module into the platform
directory and rename it to include the ABIFLAGS.
On Linux, sys.platform doesn't contain the major version anymore. It is now
always 'linux', instead of 'linux2' or 'linux3' depending on the Linux version
used to build Python.