python-native: don't cause a full regeneration of the built sources
When cross-compiling Python 2 you need a native pgen binary, but the cross
recipe can't do this on it's own so we build it in python-native and install it.
The rule to build pgen was also causing a complete rebuild of all of the
generated sources, which meant that building Python 2 needs a *host* Python 2.
This can be fixed by simply building pgen, as this is all we need to install.
[ YOCTO #13645 ]
Signed-off-by: Ross Burton <ross.burton@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
