When having this code:
```cpp
namespace {
class MyClassOutOfAnon {
public:
MyClassOutOfAnon();
} // namespace
MyClassOutOfAnon::MyClassOutOfAnon() {}
```
`MyClassOutOfAnon::MyClassOutOfAnon` is located in anonymous namespace
in `DeclContext` but outside anonymous namespace in
`LexicalDeclContext`.
For this check to work correctly, we need to check if definition is
located inside `LexicalDeclContext`.
Finds function and variable declarations inside anonymous namespace and
suggests replacing them with ``static`` declarations.
The check will enforce that
[restrict-visibility](https://llvm.org/docs/CodingStandards.html#restrict-visibility)
rule in LLVM Coding Standards is followed correctly (by adding `static`
to functions instead of putting them in anonimous namespace).
The check has additional levels of "strictness" represented by Options.
By default, the check works in the most relaxed way by giving warning
only for methods and functions defined in anonymous namespaces. Also, It
finds `static` functions that are placed inside anonymous namespace -
there is no point in keeping them inside.
