add smoothcpp (#2972)

* add smoothcpp2

* Update xmake.lua

* Update xmake.lua

* Update xmake.lua

packages/s/smoothcpp/xmake.lua

@@ -0,0 +1,28 @@
+package("smoothcpp")
+
+    set_homepage("https://github.com/heheda123123/smoothcpp")
+    set_description("Easy to use first cross platform cpp library. Intended as a supplement to the c++ standard library.")
+    set_license("MIT")
+
+    set_urls("https://github.com/heheda123123/smoothcpp.git")
+    add_versions("2023.12.20", "1ac3b09aaf2c4529d5f2bc1f4a6689c77228f02a")
+
+    on_install("windows", "mingw", "linux", "macosx", function (package)
+        local configs = {}
+        if package:config("shared") then
+            configs.kind = "shared"
+        end
+        import("package.tools.xmake").install(package, configs)
+    end)
+
+    on_test(function (package)
+        assert(package:check_cxxsnippets({test = [[
+            #include "scpp/string/string.h"
+            #include <iostream>
+
+            void test() {
+                bool a = (scpp::to_lower("aAaAAbb") == "aaaaabb");
+                std::cout << a << std::endl;
+            }
+        ]]}, {configs = {languages = "c++17"}}))
+    end)