i965: fix alpha test for MRT

Include src0 alpha in the RT write message when using MRT, so it is used
for the alpha test instead of the normal per-RT alpha value.

Fixes broken rendering in Dota2 under Wine [FDO #62647].

No Piglit regressions on Ivybridge.

V2: reuse (and simplify) existing sample_alpha_to_coverage flag in
the FS key, rather than adding another redundant one.

Signed-off-by: Chris Forbes <[email protected]>
Reviewd-by: Paul Berry <[email protected]>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=62647
NOTE: This is a candidate for the stable branches.

0 files changed, 0 insertions, 0 deletions