Add intltool as a build dependency for libgpod and run intltoolize during the build process to ensure proper macro expansion.

Formula/libgpod.rb

@@ -10,6 +10,7 @@ class Libgpod < Formula
   depends_on "libtool" => :build
   depends_on "pkg-config" => :build
   depends_on "gtk-doc" => :build
+  depends_on "intltool" => :build
 
   depends_on "glib"
   depends_on "gdk-pixbuf"
@@ -25,6 +26,10 @@ class Libgpod < Formula
     # libgpod's build system expects gtk-doc's makefile snippet to exist (gtk-doc.make),
     # which is normally provided by running gtkdocize.
     system "gtkdocize", "--copy"
+
+    # libgpod also uses intltool's Autoconf macros (IT_PROG_INTLTOOL). If intltoolize
+    # is not run, the generated ./configure may contain unexpanded macros and fail.
+    system "intltoolize", "--force", "--copy", "--automake"
     system "autoreconf", "-fiv"
 
     system "./configure", *std_configure_args,