nir/spirv: Allow loop breaks in a switch body.

Per the SPIR-V spec 2.11 Structured Control Flow:

"The only blocks in a construct that can branch outside the construct are

...
- a break block for the innermost loop it is inside of.
..."

With

"Break block: A block containing a branch to the Merge Block of a loop header's merge instruction."

Note that it puts no restriction on not being in an if or switch within the innermost loop.

This passes the loop_break block to the switch body so it can properly detect loop breaks.

CC: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/compiler/spirv/vtn_cfg.c

@@ -435,7 +435,7 @@ vtn_cfg_walk_blocks(struct vtn_builder *b, struct list_head *cf_list,
          list_for_each_entry(struct vtn_case, cse, &swtch->cases, link) {
             assert(cse->start_block != break_block);
             vtn_cfg_walk_blocks(b, &cse->body, cse->start_block, cse,
-                                break_block, NULL, loop_cont, NULL);
+                                break_block, loop_break, loop_cont, NULL);
          }
 
          /* Finally, we walk over all of the cases one more time and put