add support for (void) block expression

examples/microw8/circles.cwa

@@ -0,0 +1,20 @@
+import "env.memory" memory(4);
+
+import "env.circle" fn circle(f32, f32, f32, i32);
+import "env.sin" fn sin(f32) -> f32;
+import "env.cls" fn cls(i32);
+
+export fn tic(time: i32) {
+    cls(0);
+    let i: i32;
+    loop outer {
+        let lazy fi = i as f32 / 4 as f32;
+        let lazy t = time as f32 / 5000 as f32;
+        circle(
+            (sin(fi / 2 as f32 + t * 5 as f32) + 1 as f32) * 160 as f32,
+            (sin(fi / 3 as f32 + t * 4 as f32) + 1 as f32) * 128 as f32,
+            (sin(t * 17 as f32 + fi * 2 as f32) + 2 as f32) * 16 as f32, i * 2 + 63);
+   
+        branch_if (i := i + 1) < 63: outer
+    }
+}