disallow other type inherit from String

[firejox]

solved #3864
if we try to inherit from String, compiler will give such error

class Foo < String
end

Error in test3.cr:1: cannot inherit from String

class Foo < String
      ^

Resolves #3864

[david50407]

Any other LLVM-relatived built-in types should also forbid the inheritance?

[asterite]

@firejox This is genius!!

Could you remove the spec? It doesn't add anything, it's not testing something of the compiler. If the macro inherited is there, and it raises, that should work, we should test that.

[firejox]

@david50407 Well, LLVM-relatived built-in types are declared as struct. They cannot be inherited.

@asterite Sure :)

[asterite]

@firejox Thanks!