Add nholthaus/units v2.3.3 (#2060)

* Add nholthaus/units v2.3.3

* Address comments

* include <cassert>

* Update xmake.lua

---------

Co-authored-by: ruki <waruqi@gmail.com>

packages/u/units/xmake.lua

@@ -0,0 +1,25 @@
+package("units")
+    set_kind("library", {headeronly = true})
+    set_homepage("https://nholthaus.github.io/units/")
+    set_description("A compile-time, header-only, dimensional analysis library built on c++14 with no dependencies.")
+
+    add_urls("https://github.com/nholthaus/units/archive/refs/tags/$(version).tar.gz", "https://github.com/nholthaus/units.git")
+    add_versions("v2.3.3", "b1f3c1dd11afa2710a179563845ce79f13ebf0c8c090d6aa68465b18bd8bd5fc")
+
+    on_install(function (package)
+        os.cp("include", package:installdir())
+    end)
+
+    on_test(function (package)
+        assert(package:check_cxxsnippets({test = [[
+            #include <units.h>
+            #include <cassert>
+            static void test() {
+                constexpr units::angle::degree_t deg1{90};
+                constexpr units::angle::degree_t deg2{60};
+            
+                assert(deg1 > deg2);
+                assert(deg1 + deg2 == units::angle::degree_t{150});
+            }
+        ]]}, {configs = {languages = "c++14"}}))
+    end)