llvmpipe: disable alpha test branch if multisample is enabled.
If multisample is enabled and alpha testing happens, the branch can jump out of the fragment shader before the other samples are generated. Just don't take the branch optimisation post alpha test if multisample is enabled.
This should fix some rendering bugs in kicad with multisample enabled.
Cc: mesa-stable
Closes #6665 (closed)
Edited by Dave Airlie