Add support for Vulkan on Wayland

The variable VK_USE_PLATFORM_WAYLAND_KHR is actually used by the Vulkan
header, so use it here too.

Utilities/variant.hpp

@@ -12,6 +12,7 @@
 #include <utility>
 
 #include "recursive_wrapper.hpp"
+#include "variant_visitor.hpp"
 
 // clang-format off
 // [[deprecated]] is only available in C++14, use this for the time being
@@ -849,6 +850,22 @@ namespace std {
 				return detail::binary_dispatcher<F, V, R, Types...>::apply(v0, v1, std::forward<F>(f));
 			}
 
+			// match
+			// unary
+			template <typename... Fs>
+			auto VARIANT_INLINE match(Fs&&... fs) const
+			-> decltype(variant::visit(*this, ::std::make_visitor(std::forward<Fs>(fs)...)))
+			{
+				return variant::visit(*this, ::std::make_visitor(std::forward<Fs>(fs)...));
+			}
+			// non-const
+			template <typename... Fs>
+			auto VARIANT_INLINE match(Fs&&... fs)
+			-> decltype(variant::visit(*this, ::std::make_visitor(std::forward<Fs>(fs)...)))
+			{
+				return variant::visit(*this, ::std::make_visitor(std::forward<Fs>(fs)...));
+			}
+
 			~variant() noexcept // no-throw destructor
 			{
 				helper_type::destroy(type_index, &data);

Utilities/variant_visitor.hpp

@@ -0,0 +1,45 @@
+#ifndef MAPBOX_UTIL_VARIANT_VISITOR_HPP
+#define MAPBOX_UTIL_VARIANT_VISITOR_HPP
+
+#include <utility>
+
+//namespace mapbox {
+//namespace util {
+namespace std {
+
+template <typename... Fns>
+struct visitor;
+
+template <typename Fn>
+struct visitor<Fn> : Fn
+{
+    using Fn::operator();
+
+    template<typename T>
+    visitor(T&& fn) : Fn(std::forward<T>(fn)) {}
+};
+
+template <typename Fn, typename... Fns>
+struct visitor<Fn, Fns...> : Fn, visitor<Fns...>
+{
+    using Fn::operator();
+    using visitor<Fns...>::operator();
+
+    template<typename T, typename... Ts>
+    visitor(T&& fn, Ts&&... fns)
+        : Fn(std::forward<T>(fn))
+        , visitor<Fns...>(std::forward<Ts>(fns)...) {}
+};
+
+template <typename... Fns>
+visitor<typename std::decay<Fns>::type...> make_visitor(Fns&&... fns)
+{
+    return visitor<typename std::decay<Fns>::type...>
+        (std::forward<Fns>(fns)...);
+}
+
+}
+//} // namespace util
+//} // namespace mapbox
+
+#endif // MAPBOX_UTIL_VARIANT_VISITOR_HPP