stabilize build system: depends, installer, boost/bdb fixes, cross targets groundwork

depends/x86_64-pc-linux-gnu/include/boost/hana/fwd/is_empty.hpp

@@ -0,0 +1,49 @@
+/*!
+@file
+Forward declares `boost::hana::is_empty`.
+
+@copyright Louis Dionne 2013-2017
+Distributed under the Boost Software License, Version 1.0.
+(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+ */
+
+#ifndef BOOST_HANA_FWD_IS_EMPTY_HPP
+#define BOOST_HANA_FWD_IS_EMPTY_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/when.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! Returns whether the iterable is empty.
+    //! @ingroup group-Iterable
+    //!
+    //! Given an `Iterable` `xs`, `is_empty` returns whether `xs` contains
+    //! no more elements. In other words, it returns whether trying to
+    //! extract the tail of `xs` would be an error. In the current version
+    //! of the library, `is_empty` must return an `IntegralConstant` holding
+    //! a value convertible to `bool`. This is because only compile-time
+    //! `Iterable`s are supported right now.
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/is_empty.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    constexpr auto is_empty = [](auto const& xs) {
+        return tag-dispatched;
+    };
+#else
+    template <typename It, typename = void>
+    struct is_empty_impl : is_empty_impl<It, when<true>> { };
+
+    struct is_empty_t {
+        template <typename Xs>
+        constexpr auto operator()(Xs const& xs) const;
+    };
+
+    constexpr is_empty_t is_empty{};
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FWD_IS_EMPTY_HPP