python: Fix float byte order detection

python: Fix float byte order detection

This backports patches from bpo-34585[1] to fix byte order detection of
floats.

Fixing byte order detection allows the repr() of floats to be shorter (a
feature backported to Python 2.7 from Python 3.1[2]).
sys.float_repr_style should be 'short' instead of 'legacy' on supported
platforms.

See #11134.

[1]: https://bugs.python.org/issue34585
[2]: https://docs.python.org/2.7/whatsnew/2.7.html#python-3-1-features

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