Sema: validate equality on store to comptime field

test/cases/compile_errors/invalid_store_to_comptime_field.zig

@@ -0,0 +1,20 @@
+pub export fn entry() void {
+    const S = struct {
+        comptime a: [2]u32 = [2]u32{ 1, 2 },
+    };
+    var s: S = .{};
+    s.a = [2]u32{ 2, 2 };
+}
+pub export fn entry1() void {
+    const T = struct { a: u32, b: u32 };
+    const S = struct {
+        comptime a: T = T{ .a = 1, .b = 2 },
+    };
+    var s: S = .{};
+    s.a = T{ .a = 2, .b = 2 };
+}
+// error
+// backend=stage2,llvm
+//
+// :6:19: error: value stored in comptime field does not match the default value of the field
+// :14:19: error: value stored in comptime field does not match the default value of the field