boost189: move cygwin patch to generic.nix

Since #495346, `boost189.override { patches = ...; }` does not work as expected.

pkgs/development/libraries/boost/1.89.nix

@@ -1,10 +1,4 @@
-{
-  lib,
-  stdenv,
-  callPackage,
-  fetchurl,
-  ...
-}@args:
+{ callPackage, fetchurl, ... }@args:
 
 callPackage ./generic.nix (
   args
@@ -21,7 +15,5 @@ callPackage ./generic.nix (
       # SHA256 from http://www.boost.org/users/history/version_1_89_0.html
       sha256 = "85a33fa22621b4f314f8e85e1a5e2a9363d22e4f4992925d4bb3bc631b5a0c7a";
     };
-
-    patches = lib.optional stdenv.hostPlatform.isCygwin ./Fix-cygwin-build-189.patch;
   }
 )

pkgs/development/libraries/boost/generic.nix

@@ -258,7 +258,10 @@ stdenv.mkDerivation {
     ]
     ++ lib.optional (
       stdenv.hostPlatform.isCygwin && lib.versionAtLeast version "1.87" && lib.versionOlder version "1.88"
-    ) ./Fix-cygwin-build-187.patch;
+    ) ./Fix-cygwin-build-187.patch
+    ++ lib.optional (
+      stdenv.hostPlatform.isCygwin && lib.versionAtLeast version "1.89" && lib.versionOlder version "1.90"
+    ) ./Fix-cygwin-build-189.patch;
 
   meta = {
     homepage = "http://boost.org/";