gnu: xdg-desktop-portal: Update to 1.8.1 and honor XDG_DESKTOP_PORTAL_DIR.

* gnu/packages/freedesktop.scm (xdg-desktop-portal): Update to 1.8.1.
[arguments, native-search-paths]: New field.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

gnu/packages/freedesktop.scm

@@ -2269,7 +2269,7 @@ fallback to generic Systray support if none of those are available.")
 (define-public xdg-desktop-portal
   (package
     (name "xdg-desktop-portal")
-    (version "1.7.2")
+    (version "1.8.1")
     (source (origin
               (method git-fetch)
               (uri (git-reference
@@ -2278,7 +2278,7 @@ fallback to generic Systray support if none of those are available.")
               (file-name (git-file-name name version))
               (sha256
                (base32
-                "0rkwpsmbn3d3spkzc2zsd50l2r8pp4la390zcpsawaav8w7ql7xm"))))
+                "0pq0kmvzk56my396vh97pzw4wizwmlmzvv2kr2xv047x3044mr5n"))))
     (build-system gnu-build-system)
     (native-inputs
      `(("pkg-config" ,pkg-config)
@@ -2298,6 +2298,21 @@ fallback to generic Systray support if none of those are available.")
        ("geoclue" ,geoclue)
        ("pipewire" ,pipewire-0.3)
        ("fuse" ,fuse)))
+    (arguments
+     `(#:phases
+       (modify-phases %standard-phases
+         (add-after 'unpack 'po-chmod
+           (lambda _
+             ;; Make sure 'msgmerge' can modify the PO files.
+             (for-each (lambda (po)
+                         (chmod po #o666))
+                       (find-files "po" "\\.po$"))
+             #t)))))
+    (native-search-paths
+     (list (search-path-specification
+            (variable "XDG_DESKTOP_PORTAL_DIR")
+            (separator #f)
+            (files '("share/xdg-desktop-portal/portals")))))
     (home-page "https://github.com/flatpak/xdg-desktop-portal")
     (synopsis "Desktop integration portal for sandboxed apps")
     (description