python3: generate reproducible .pyc

python3: generate reproducible .pyc

.pyc files contain the modification time of the corresponding .py
source. In order to make the build reproducible, we fix the modification
time of all .py before compiling .pyc files.

In addition, since pycompile relies on the modification time to know if
a file needs to be recompiled, it is safer to force recompilation of all
source files.

This work was sponsored by `BA Robotic Systems'.

Signed-off-by: Jérôme Pouiller <jezz@sysmic.org>
Reviewed-by: Samuel Martin <s.martin49@gmail.com>
[Thomas: do not register PYTHON_FIX_TIME as a
 PYTHON_TARGET_FINALIZE_HOOKS, instead call it inside
 PYTHON_CREATE_PYC_FILES before doing the byte compilation.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>