Problem: no support for ZMTP 3.1 application metadata

Migrate more tests to unity

Solution: add unity dependencies/flags

Solution: migrate to unity

Solution: split up test case

Solution: migrate to unity

Problem: test assertion failures do not clean up properly

Lets the application set per-connection metadata.
Metadata is specified as "X-key:value" and set using zmq_setsockopt, eg:
zmq_setsockopt (s, ZMQ_METADATA, "X-key:value", 11);

The peer can then obtain the metadata from a received message:
char *data = zmq_msg_gets(msg, "X-key");

Solution: add guidelines to tests/README.md

Solution: provide test_context and manage sockets of test_context via setup and teardown

Migrate further tests (test_hwm, test_router_mandatory) to unity

Solution: removed

Solution: fixed description for building tests, added references to unity and unittests

Solution: migrate to unity

Missing IMPORTED_LOCATION_<CONFIG>property for shared-library import-targets (see zeromq/libzmq#2985)

Fixes for mingw cross-compilation

Solution: remove objects optimisation in library build (similar to #2860)
and set PUBLIC compile definitions on all static builds instead of MSVC
only.

* Fixes issue 2963, ref stream_engine.cpp:981

* Fixes issue 2963, ref socks_connecter.cpp:158

* Fixes issue 2963, ref tcp_listener.cpp:144

* Fixes issue 2963, ref tcp_connecter.cpp:423

* Fixes issue 2963, ref socks_connecter.cpp:436

* Fixes issue 2963, ref tcp_listener.cpp:179

* Fixes issue 2963, ref tcp_listener.cpp:268

* Fixes issue 2963, ref tcp_connecter.cpp:160

Solution: change case of `WinSock2.h Iphlpapi.h Rpc.h` to match the
files on disk. This is only noticeable when cross-compiling from a
case-sensitive system so wouldn't get picked up in MSVC or mingw
builds running on a windows machine.

MSDN uses capitalised versions in prose and lowercase in code examples:
https://msdn.microsoft.com/en-us/library/windows/desktop/ms737629(v=vs.85).aspx

Fixes #2978, the missing library message is a little misleading.

Problem: formatting issues in CI

Solution: commit clang-format-diff

Solution: add pragma to make clang-format ignore the external code

* Problem: Still need to port over more files to VxWorks 6.x

Solution: Port more files to VxWorks 6.x

* Problem: Need to port over remaining files to VxWorks 6.x. Also remove POSIX thread dependency for VxWorks (because of priority inversion problem in POSIX mutexes with VxWorks 6.x processes)

Solution: Port over remaining files to VxWorks 6.x. Also removed POSIX thread dependency for VxWorks

* Problem: Needed to modify TCP, UDP, TIPC classes with #ifdefs to be compatible with VxWorks 6.x.

Solution:  Modify TCP, UDP, TIPC classes with #ifdefs to be compatible with VxWorks 6.x

Fixed issue #2979

* Problem: TIPC availability check is too strict

Solution: at build time only check if the API is available. In the tests
do a first check and a skip if the functionality is not available.

TIPC needs an in-tree but not loaded by default kernel module, tipc.ko
to be loaded, which requires root, so it is unlikely to be available on
any build system by default.
This will allow most distributions to ship with TIPC support built in,
and to avoid tests failure if the module is not there.

* Problem: no Travis tests for TIPC

Solution: mark one job with sudo: required and load the kernel module

* Problem: CMake fails when test returns 77 (skip)

Solution: set property to let it mark the test as skipped as intended

* Tests for different TIPC address types and code cleanup

* Adds tests for binding/connecting with different TIPC address types
  using Unity
* Adds error checking for address type misuse

Revert "Problem: mis-detection of threadsafe_static_init causes test failures"

Problem: mis-detection of threadsafe_static_init causes test failures

Solution: do not rely __cplusplus >= 201103L to detect whether the
compiler supports thread safe static initialisation, but check only
the proper feature preprocessor macro.
GCC introduced it in version 8, and Clang in version 6.

Problem: build broken with gcc-4.7

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]

Problem: code duplication in getsockopt/setsockopt