package/zmqpp: add patch to fix build issue

Add a patch from upstream to fix build error:
  error: no match for 'operator<<'

Fixes:
http://autobuild.buildroot.net/results/ed4508a00663b03632a4eb9411ba05852d02fd88/

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/zmqpp/zmqpp.hash

@@ -1,2 +1,3 @@
 # Locally calculated
 sha256	92cb5bf7e1df8b99792fe1eb530bf91fced9c2d14159007bec011bb1b8248269  zmqpp-3.2.0.tar.gz
+sha256	0b76169a48a0ba9dd581b63787b4852f3922de0c22b7a325cab688c1bafb3dd7  260a9304f6c74272bd3c396f6cca685657b4aff1.patch

package/zmqpp/zmqpp.mk

@@ -10,6 +10,7 @@ ZMQPP_INSTALL_STAGING = YES
 ZMQPP_DEPENDENCIES = zeromq
 ZMQPP_LICENSE = MIT
 ZMQPP_LICENSE_FILES = LICENSE
+ZMQPP_PATCH = https://github.com/zeromq/zmqpp/commit/260a9304f6c74272bd3c396f6cca685657b4aff1.patch
 
 ZMQPP_MAKE_OPTS = LD="$(TARGET_CXX)" BUILD_PATH=./build PREFIX=/usr
 ZMQPP_LDFLAGS = $(TARGET_LDFLAGS) -lpthread