Move to python3 host tool compiliation

[Christian Marangi (Ansuel)]

Hi all,

This is mostly feedback request on a change I would like to merge.
This is the PR in question [1].

It transition from using host python3 to compile one from source.

The reason is simple. We had multiple times where things ""explode""
as the symbolic link for python gets corrupted after a python version
update.

This got even more relevant recently as they started to spam new
versions of python almost weekly.

To solve this problem once and for all (also also have a more
predictable host tools) we compile python from source and
use our version directly without depending on the one present
on the host.

The compilation increase is minimal and also we still provide an
option to use the previous implementation of using the host python.

Is anyone against this change or do you find any problem?

Feel free to give any opinion here, the main object of this is to stop
the periodic complain of "my buildroot installation broke and I
can't compile anything anymore"

[1] https://github.com/openwrt/openwrt/pull/10800