cygwin-dll-link: use link for cygwin1.dll

pkgs/os-specific/cygwin/cygwin-dll-link-hook/cygwin-dll-link.sh

@@ -29,7 +29,11 @@ _linkDeps() {
   local dll
   _dllDeps "$target" | while read -r dll; do
     echo '  dll:' "$dll"
-    if [[ -e "$dir/$dll" ]]; then continue; fi
+    if [[ -L "$dir/$dll" || -e "$dir/$dll" ]]; then continue; fi
+    if [[ $dll = cygwin1.dll ]]; then
+      CYGWIN+=\ winsymlinks:nativestrict ln -sr /bin/cygwin1.dll "$dir"
+      continue
+    fi
     # Locate the DLL - it should be an *executable* file on $LINK_DLL_FOLDERS.
     local dllPath
     if ! dllPath="$(PATH="$(dirname "$target"):$LINK_DLL_FOLDERS" type -P "$dll")"; then

pkgs/stdenv/generic/make-derivation.nix

@@ -704,7 +704,6 @@ let
               allowedImpureDLLs
               ++ lib.optionals isCygwin [
                 "KERNEL32.dll"
-                "cygwin1.dll"
               ];
           }
           // (