Add assertions for matches that used to use analyze_branch (#5733)

Following up from #5730, add debug assertions to ensure that new branch instructions don't slip through matches that used to use analyze_branch.

cranelift/codegen/src/inst_predicates.rs

@@ -204,7 +204,7 @@ pub(crate) fn visit_block_succs<F: FnMut(Inst, Block, bool)>(
                 }
             }
 
-            _ => {}
+            inst => debug_assert!(!inst.opcode().is_branch()),
         }
     }
 }