Add compile error test for struct layout depending on being pointer aligned.

Move circular dependency tests into struct / union tests.

Author: kcbanner

test/behavior/container_circular_dependency.zig

@@ -1803,3 +1803,22 @@ test "initializer takes a pointer to a variable inside its struct" {
     try namespace.doTheTest();
     comptime try namespace.doTheTest();
 }
+
+const StructInner = extern struct {
+    outer: StructOuter = std.mem.zeroes(StructOuter),
+};
+
+const StructMiddle = extern struct {
+    outer: ?*StructInner,
+    inner: ?*StructOuter,
+};
+
+const StructOuter = extern struct {
+    middle: StructMiddle = std.mem.zeroes(StructMiddle),
+};
+
+test "circular dependency through pointer field of a struct" {
+    var outer: StructOuter = .{};
+    try expect(outer.middle.outer == null);
+    try expect(outer.middle.inner == null);
+}

test/behavior/struct.zig

@@ -2001,3 +2001,22 @@ test "union field is a pointer to an aligned version of itself" {
 
     try expect(&e == e.next);
 }
+
+const UnionInner = extern struct {
+    outer: UnionOuter = std.mem.zeroes(UnionOuter),
+};
+
+const UnionMiddle = extern union {
+    outer: ?*UnionOuter,
+    inner: ?*UnionInner,
+};
+
+const UnionOuter = extern struct {
+    u: UnionMiddle = std.mem.zeroes(UnionMiddle),
+};
+
+test "circular dependency through pointer field of a union" {
+    var outer: UnionOuter = .{};
+    try expect(outer.u.outer == null);
+    try expect(outer.u.inner == null);
+}

test/behavior/union.zig

@@ -0,0 +1,11 @@
+const S = struct {
+    next: ?*align(1) S align(128),
+};
+
+export fn entry() usize {
+    return @alignOf(S);
+}
+
+// error
+//
+// :1:11: error: struct layout depends on being pointer aligned