gnome-maps: fix cross compilation

upstream determines the gjs path with `find_program('gjs')`, however
this fails to find anything when cross compiling because meson doesn't
know which paths to check.

the interaction between meson's `find_program` and `cross-file` is
documented here:
<https://mesonbuild.com/Reference-manual_functions.html#find_program>

pkgs/by-name/gn/gnome-maps/package.nix

@@ -25,6 +25,7 @@
   libadwaita,
   geocode-glib_2,
   tzdata,
+  writeText,
 }:
 
 stdenv.mkDerivation (finalAttrs: {
@@ -68,6 +69,13 @@ stdenv.mkDerivation (finalAttrs: {
     libsoup_3
   ];
 
+  mesonFlags = [
+    "--cross-file=${writeText "crossfile.ini" ''
+      [binaries]
+      gjs = '${lib.getExe gjs}'
+    ''}"
+  ];
+
   preCheck = ''
     # “time.js” included by “timeTest” and “translationsTest” depends on “org.gnome.desktop.interface” schema.
     export XDG_DATA_DIRS="${gsettings-desktop-schemas}/share/gsettings-schemas/${gsettings-desktop-schemas.name}:$XDG_DATA_DIRS"