boost_sml: add package (#2569)

* boost_sml: add package

* fix languages

packages/b/boost_sml/xmake.lua

@@ -0,0 +1,29 @@
+package("boost_sml")
+    set_kind("library", {headeronly = true})
+    set_homepage("https://boost-ext.github.io/sml")
+    set_description("SML: C++14 State Machine Library")
+    set_license("BSL-1.0")
+
+    add_urls("https://github.com/boost-ext/sml/archive/refs/tags/$(version).tar.gz",
+             "https://github.com/boost-ext/sml.git")
+
+    add_versions("v1.1.8", "d2626b2fd249fa0788ca364a2f8dcb4762dd72195f86d43370e4cad4c02262c5")
+
+    add_deps("cmake")
+
+    on_install(function (package)
+        import("package.tools.cmake").install(package, configs)
+    end)
+
+    on_test(function (package)
+        assert(package:check_cxxsnippets({test = [[
+            #include <boost/sml.hpp>
+            namespace sml = boost::sml;
+            struct e2 {
+                bool value = true;
+            };
+            void test() {
+                auto event2 = sml::event<e2>;
+            }
+        ]]}, {configs = {languages = "c++20"}}))
+    end)