improve libpng

packages/l/libpng/xmake.lua

@@ -20,7 +20,10 @@ package("libpng")
     end
  
     on_install("windows", function (package)
-        import("package.tools.cmake").install(package)
+        local configs = {"-DPNG_TESTS=OFF",
+                         "-DPNG_SHARED=OFF", 
+                         "-DPNG_DEBUG=" .. package:debug() and "ON" or "OFF"}
+        import("package.tools.cmake").install(package, configs)
     end)
 
     on_install("macosx", "linux", function (package)