radeonsi: disable sinking common instructions down to the end block

radeonsi: disable sinking common instructions down to the end block

Initially this was a workaround for a bug introduced in LLVM 4.0
in the SimplifyCFG pass that caused image instrinsics to disappear
(because they were badly sunk). Finally, this is a win because it
decreases SGPR spilling and increases the number of waves a bit.

Although, shader-db results are good I think we might want to
remove it in the future once the issue is fixed. For now, enable
it for LLVM >= 4.0.

This also fixes a rendering issue with the speedometer in Dirt Rally.

More information can be found here https://reviews.llvm.org/D26348.

Thanks to Dave Airlie for the patch.

v2: - add a FIXME comment
    - use if (HAVE_LLVM >= 0x0400) instead

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99484
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97988
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Cc: 17.0 <mesa-stable@lists.freedesktop.org>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>