Only accelerate python if explicitly requested

Python accel requires export SBOX_REDIRECT_FORCE=/usr/bin/python

Signed-off-by: Juha Kallioinen <juha.kallioinen@jollamobile.com>
Add conditional acceleration for doxygen

Only accelerate doxygen if it can be found from the target root

Signed-off-by: Juha Kallioinen <juha.kallioinen@jollamobile.com>