CFLAGS output of pkg-config not used for libzmq #6764
Description
When libzmq is installed in a non-standard location (and PKG_CONFIG_PATH is set appropriately) the Makefile does not make use of ZMQ_CFLAGS and consequently the make fails with:
CXX zmq/libbitcoin_zmq_a-zmqabstractnotifier.o
In file included from zmq/zmqabstractnotifier.h:8:0,
from zmq/zmqabstractnotifier.cpp:5:
zmq/zmqconfig.h:16:17: fatal error: zmq.h: No such file or directory
#include <zmq.h>
^
compilation terminated.