Make Badge constructors noexcept
Make Badge constructors noexcept

Summary:
Make `folly::badge` and `folly::any_badge` noexcept constructible.
Cannot make constructors explicitly defaulted due to classes becoming aggregate types.
Aggregate type construction takes precedence over value constructors so we can construct them anywhere:
```
class A{
    A() = default;
};

int main() {
    A a = {};
}
```
Cannot mark them `explicit` either, since we prefer to have conversions auto-magical where possible.

Reviewed By: yfeldblum

Differential Revision: D31983342

fbshipit-source-id: ddeffc30e6332882a490afea5bf023522f96c18e

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly