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

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

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+/*!
+@file
+Defines `boost::hana::flatten`.
+
+@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_FLATTEN_HPP
+#define BOOST_HANA_FLATTEN_HPP
+
+#include <boost/hana/fwd/flatten.hpp>
+
+#include <boost/hana/concept/monad.hpp>
+#include <boost/hana/concept/sequence.hpp>
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/dispatch.hpp>
+#include <boost/hana/core/make.hpp>
+#include <boost/hana/detail/unpack_flatten.hpp>
+#include <boost/hana/functional/id.hpp>
+#include <boost/hana/fwd/chain.hpp>
+
+#include <cstddef>
+#include <utility>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! @cond
+    template <typename Xs>
+    constexpr auto flatten_t::operator()(Xs&& xs) const {
+        using M = typename hana::tag_of<Xs>::type;
+        using Flatten = BOOST_HANA_DISPATCH_IF(flatten_impl<M>,
+            hana::Monad<M>::value
+        );
+
+#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
+        static_assert(hana::Monad<M>::value,
+        "hana::flatten(xs) requires 'xs' to be a Monad");
+#endif
+
+        return Flatten::apply(static_cast<Xs&&>(xs));
+    }
+    //! @endcond
+
+    template <typename M, bool condition>
+    struct flatten_impl<M, when<condition>> : default_ {
+        template <typename Xs>
+        static constexpr auto apply(Xs&& xs)
+        { return hana::chain(static_cast<Xs&&>(xs), hana::id); }
+    };
+
+    template <typename S>
+    struct flatten_impl<S, when<Sequence<S>::value>> {
+        template <typename Xs>
+        static constexpr auto apply(Xs&& xs) {
+            return detail::unpack_flatten(static_cast<Xs&&>(xs), hana::make<S>);
+        }
+    };
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FLATTEN_HPP