add libspng (#711)

* add libspng

* Update xmake.lua

* Update xmake.lua

packages/l/libspng/xmake.lua

@@ -0,0 +1,42 @@
+package("libspng")
+
+    set_homepage("https://libspng.org")
+    set_description("Simple, modern libpng alternative")
+
+    set_urls("https://github.com/randy408/libspng/archive/refs/tags/$(version).tar.gz",
+             "https://github.com/randy408/libspng.git")
+    add_versions("v0.7.1", "0726a4914ad7155028f3baa94027244d439cd2a2fbe8daf780c2150c4c951d8e")
+
+    add_deps("zlib")
+
+    on_load(function (package)
+        if not package:config("shared") then
+            package:add("defines", "SPNG_STATIC")
+        end
+    end)
+
+    on_install(function (package)
+        io.writefile("xmake.lua", [[
+            add_rules("mode.debug", "mode.release")
+            add_requires("zlib")
+            target("spng")
+                set_kind("$(kind)")
+                add_files("spng/*.c")
+                add_headerfiles("spng/*.h")
+                add_packages("zlib")
+                if is_kind("static") then
+                    add_defines("SPNG_STATIC")
+                end
+        ]])
+        local configs = {}
+        if package:config("shared") then
+            configs.kind = "shared"
+        elseif not package:is_plat("windows", "mingw") and package:config("pic") ~= false then
+            configs.cxflags = "-fPIC"
+        end
+        import("package.tools.xmake").install(package, configs)
+    end)
+
+    on_test(function (package)
+        assert(package:has_cfuncs("spng_decode_image", {includes = "spng.h"}))
+    end)