Assert when struct size would exceed 4 GB.

test/test_suite/struct/struct_too_large.c3

@@ -0,0 +1,12 @@
+import std;
+struct Foo
+{
+    int a;
+    int[int.max] b; // #error: "Struct member 'b' would cause the struct to become too large
+}
+
+fn int main()
+{
+    Foo c = (Foo){};
+    return 0;
+}