shader: Add more tests about 'for' loops

internal/shader/testdata/for3.expected.vs

@@ -0,0 +1,20 @@
+void F0(out vec2 l0);
+
+void F0(out vec2 l0) {
+	vec2 l1 = vec2(0);
+	vec2 l3 = vec2(0);
+	l1 = vec2(0.0);
+	for (int l2 = 0; l2 < 100; l2++) {
+		vec2 l5 = vec2(0);
+		l3 = vec2(0.0);
+		l1 = l3;
+	}
+	l3 = vec2(0.0);
+	for (int l4 = 0; l4 < 100; l4++) {
+		vec2 l5 = vec2(0);
+		l5 = vec2(0.0);
+		l3 = l5;
+	}
+	l0 = l1;
+	return;
+}

internal/shader/testdata/for3.go

@@ -0,0 +1,15 @@
+package main
+
+func Foo() vec2 {
+	v := vec2(0)
+	for i := 0; i < 100; i++ {
+		v2 := vec2(0)
+		v = v2
+	}
+	v3 := vec2(0)
+	for i := 0; i < 100; i++ {
+		v4 := vec2(0)
+		v3 = v4
+	}
+	return v
+}