Solution: initialise variable in options.cpp to dummy value to fix
compiler complaint:

 src/options.cpp: In function
  'int zmq::do_setsockopt_int_as_bool_strict(const void*, size_t, bool*)':
 src/options.cpp:121:5: error: 'value' may be used uninitialized in
  this function [-Werror=maybe-uninitialized]
 src/options.cpp: In function
  'int zmq::do_setsockopt_int_as_bool_relaxed(const void*, size_t, bool*)':
 src/options.cpp:135:31: error: 'value' may be used uninitialized in
  this function [-Werror=maybe-uninitialized]