[clang-tidy] Add a checker for code that looks like a delegate constructors but doesn't delegate.

Summary:
class Foo {
  Foo() {
    Foo(42); // oops
  }
  Foo(int);
};

This is valid code but it does nothing and we can't emit a warning in clang
because there might be side effects. The checker emits a warning for this
pattern and also for base class initializers written in this style.

There is some overlap with the unused-rtti checker but they follow different
goals and fire in different places most of the time.

Reviewers: alexfh, djasper

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D4667

llvm-svn: 214397