intel/compiler: Don't predicate a WHILE if there is a CONT

intel/compiler: Don't predicate a WHILE if there is a CONT

Previously a predicated BREAK that appeared immediately before the WHILE
would get merged into the WHILE.  This doesn't work if other flow
control (e.g., a CONT) can transfer directly to the WHILE.

On Intel platforms, this fixes the CTS test
dEQP-VK.graphicsfuzz.stable-binarysearch-tree-nested-if-and-conditional.

No shader-db changes on any Intel platform.

When this commit was first created (over a month before it is going to
land), there were some regressions that were prevented by other commits
in MR !13095.  That does not appear to be the case now, so I don't know
what changed.  Basically, the treatment of discard as a combination of
demote and terminate causes additional continues in some loops, and
those continues trigger this bug.  The other commits from that MR
prevent those continues from being generated in the first place.

All Intel platforms had simlar fossil-db results. (Ice Lake shown)
Instructions in all programs: 144419989 -> 144419995 (+0.0%)
SENDs in all programs: 6947332 -> 6947332 (+0.0%)
Loops in all programs: 38277 -> 38277 (+0.0%)
Spills in all programs: 204075 -> 204075 (+0.0%)
Fills in all programs: 319480 -> 319480 (+0.0%)

A few shaders in Doom 2016 were hurt by one instruction each.  It seems
likely that these shaders would have experienced at least some
mis-rendering.

Closes: #4213
Fixes: d13bcdb3a9f ("i965/fs: Extend predicated break pass to predicate WHILE.")
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14128>