gem-config: fix zookeeper for gcc-8 (#68642)

pkgs/development/ruby-modules/gem-config/default.nix

@@ -19,7 +19,7 @@
 
 { lib, fetchurl, writeScript, ruby, kerberos, libxml2, libxslt, python, stdenv, which
 , libiconv, postgresql, v8_3_16_14, clang, sqlite, zlib, imagemagick
-, pkgconfig , ncurses, xapian, gpgme, utillinux, fetchpatch, tzdata, icu, libffi
+, pkgconfig , ncurses, xapian, gpgme, utillinux, tzdata, icu, libffi
 , cmake, libssh2, openssl, mysql, darwin, git, perl, pcre, gecode_3, curl
 , msgpack, qt59, libsodium, snappy, libossp_uuid, lxc, libpcap, xorg, gtk2, buildRubyGem
 , cairo, re2, rake, gobject-introspection, gdk-pixbuf, zeromq, czmq, graphicsmagick, libcxx
@@ -613,5 +613,11 @@ in
 
   zookeeper = attrs: {
     buildInputs = stdenv.lib.optionals stdenv.isDarwin [ darwin.cctools ];
+    dontBuild = false;
+    postPatch = ''
+      sed -i ext/extconf.rb -e "4a \
+        FileUtils.cp '${./zookeeper-ftbfs-with-gcc-8.patch}', 'patches/zkc-3.4.5-gcc-8.patch'
+      "
+    '';
   };
 }