explicitely remove gtk-doc.make if gtkdoc is not installed

autogen.sh

@@ -12,6 +12,8 @@ mkdir m4 2>/dev/null
 GTKDOCIZE=`which gtkdocize 2>/dev/null`
 if test $? -ne 0; then
   echo "No gtk-doc support found. You can't build the docs."
+  # rm because gtk-doc.make might be a link to a protected file
+  rm -f gtk-doc.make 2>/dev/null
   echo "EXTRA_DIST =" >gtk-doc.make
   echo "CLEANFILES =" >>gtk-doc.make
   GTKDOCIZE=""