more uniform directory structure: Windows DLLs are treated like binaries;

--- a/src/Pure/Admin/component_polyml.scala	Sat Apr 12 19:05:31 2025 +0200
+++ b/src/Pure/Admin/component_polyml.scala	Sat Apr 12 19:14:54 2025 +0200
@@ -90,6 +90,12 @@
       "make check",
       "make install")
 
+    if (platform.is_windows) {
+      val bin_dir = target_dir + Path.explode("bin")
+      val lib_dir = target_dir + Path.explode("lib")
+      Isabelle_System.copy_dir(bin_dir, lib_dir, direct = true)
+    }
+
     progress.echo("GMP installation directory: " + target_dir)
     target_dir
   }