[Piglit] llvm7 / radeonsi: Regression on some fragment shaders: black screen - The 'undefs' are processed as 'NaN'.

[patrick9876 at free.fr]

Did you have issues on some fragments shaders like: 
https://www.shadertoy.com/view/ltl3WS or 
https://www.shadertoy.com/view/MdVcRd ?

These shaders are now displaying a black screen.


More details here:
https://bugs.freedesktop.org/show_bug.cgi?id=109608