calls: fix cross compilation

gtkdoc invokes the host `calls` binary to build documentation.
that's fixed here by providing an emulator; the no-emulator alternative
is `-Dgtk_doc=false` in `mesonFlags`.

pkgs/by-name/ca/calls/package.nix

@@ -3,6 +3,7 @@
   stdenv,
   fetchFromGitLab,
   meson,
+  mesonEmulatorHook,
   ninja,
   pkg-config,
   libadwaita,
@@ -51,19 +52,23 @@ stdenv.mkDerivation (finalAttrs: {
     "devdoc"
   ];
 
-  nativeBuildInputs = [
-    meson
-    ninja
-    pkg-config
-    desktop-file-utils
-    appstream-glib
-    vala
-    wrapGAppsHook4
-    gtk-doc
-    docbook-xsl-nons
-    docbook_xml_dtd_43
-    docutils
-  ];
+  nativeBuildInputs =
+    [
+      meson
+      ninja
+      pkg-config
+      desktop-file-utils
+      appstream-glib
+      vala
+      wrapGAppsHook4
+      gtk-doc
+      docbook-xsl-nons
+      docbook_xml_dtd_43
+      docutils
+    ]
+    ++ lib.optionals (!stdenv.buildPlatform.canExecute stdenv.hostPlatform) [
+      mesonEmulatorHook
+    ];
 
   buildInputs = [
     modemmanager