libmemcached: fix linking with libpthread

Add patch to fix linking against libpthread (from Fedora).

https://bugzilla.redhat.com/show_bug.cgi?id=1037707
https://bugs.launchpad.net/libmemcached/+bug/1281907

This fixes (upcoming) libmemcached use in collectd, which currently
doesn't work because of link failure caused by missing "pthread_once"
symbol.

pkgs/development/libraries/libmemcached/default.nix

@@ -8,6 +8,11 @@ stdenv.mkDerivation rec {
     sha256 = "10jzi14j32lpq0if0p9vygcl2c1352hwbywzvr9qzq7x6aq0nb72";
   };
   
+  # Fix linking against libpthread (patch from Fedora)
+  # https://bugzilla.redhat.com/show_bug.cgi?id=1037707
+  # https://bugs.launchpad.net/libmemcached/+bug/1281907
+  patches = [ ./libmemcached-fix-linking-with-libpthread.patch ];
+
   buildInputs = [ cyrus_sasl libevent ];
 
   meta = {