bug#40406: python-matplotlib fails to build on i686-linux

[Diego Nicola Barbato <dnbarbato@posteo.de>]

Hi Guix,

The package python-matplotlib fails to build during the check phase on
i686-linux.  The test failure appears to be deterministic:

--8<---------------cut here---------------start------------->8---
=================================== FAILURES ===================================
_______________________ test_slider_horizontal_vertical ________________________

    def test_slider_horizontal_vertical():
        fig, ax = plt.subplots()
        slider = widgets.Slider(ax=ax, label='', valmin=0, valmax=24,
                                valinit=12, orientation='horizontal')
        slider.set_val(10)
        assert slider.val == 10
        # check the dimension of the slider patch in axes units
        box = slider.poly.get_extents().transformed(ax.transAxes.inverted())
>       assert_allclose(box.bounds, [0, 0, 10/24, 1])
E       AssertionError: 
E       Not equal to tolerance rtol=1e-07, atol=0
E       
E       Mismatch: 25%
E       Max absolute difference: 1.11022302e-16
E       Max relative difference: 2.66453526e-16
E        x: array([ 0.000000e+00, -2.310706e-18,  4.166667e-01,  1.000000e+00])
E        y: array([0.      , 0.      , 0.416667, 1.      ])

/gnu/store/8g8yfikj63wf0y3hwvpk00hqj5wpfs7v-python-matplotlib-3.1.2/lib/python3.7/site-packages/matplotlib/tests/test_widgets.py:333: AssertionError
--8<---------------cut here---------------end--------------->8---

Im currently on commit 151f3d4.

Regards,

Diego