CFG exhaustive when else instruction for KT-8700

compiler/testData/cfg-variables/basic/ExhaustiveInitialization.kt

@@ -0,0 +1,14 @@
+enum class Direction {
+    NORTH, SOUTH, WEST, EAST
+}
+
+fun foo(dir: Direction): Int {
+    val res: Int
+    when (dir) {
+        Direction.NORTH -> res = 1
+        Direction.SOUTH -> res = 2
+        Direction.WEST  -> res = 3
+        Direction.EAST  -> res = 4
+    }
+    return res
+}