radv: disable the auto-waitcnt-before-barrier LLVM option

radv: disable the auto-waitcnt-before-barrier LLVM option

This option allows us to remove additional s_waitcnt instructions
because s_barrier internally does s_waitcnt 0.

Though, apparently there is a problem with LDS accesses that
causes rendering issues with FFXV and DXVK. Disable this
optimization for now (RadeonSI still uses it).

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107460
CC: 18.2 <mesa-stable@lists.freedesktop.org>
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>