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

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

@@ -0,0 +1,57 @@
+/*!
+@file
+Forward declares `boost::hana::if_`.
+
+@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_IF_HPP
+#define BOOST_HANA_FWD_IF_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/when.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! Conditionally return one of two values based on a condition.
+    //! @ingroup group-Logical
+    //!
+    //! Specifically, `then` is returned iff `cond` is true-valued, and
+    //! `else_` is returned otherwise. Note that some `Logical` models may
+    //! allow `then` and `else_` to have different types, while others may
+    //! require both values to have the same type.
+    //!
+    //!
+    //! @param cond
+    //! The condition determining which of the two values is returned.
+    //!
+    //! @param then
+    //! The value returned when `cond` is true-valued.
+    //!
+    //! @param else_
+    //! The value returned when `cond` is false-valued.
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/if.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    constexpr auto if_ = [](auto&& cond, auto&& then, auto&& else_) -> decltype(auto) {
+        return tag-dispatched;
+    };
+#else
+    template <typename L, typename = void>
+    struct if_impl : if_impl<L, when<true>> { };
+
+    struct if_t {
+        template <typename Cond, typename Then, typename Else>
+        constexpr decltype(auto) operator()(Cond&& cond, Then&& then, Else&& else_) const;
+    };
+
+    constexpr if_t if_{};
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FWD_IF_HPP