This changes Build/InstallDev for both Python 2 and 3 to only copy files
from target Python, not from host Python, since InstallDev files are
used for target packages to link to other target packages.

In particular, usr/lib/python{2.7,3.7}/_sysconfigdata.py holds system
configuration data generated at build time, and is different for target
Python and host Python.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>