Solution: change return type to int (again) and return fd via an output parameter

Solution: use proper fd_t type, and also define and use a zmq_fd_t in the API

Problem: generated ZeroMQConfig.cmake does not work when only static …

Solution: check for availability of shared/static libzmq targets

Some cleanup in CMakeLists.txt

Solution: use check_cxx_symbol_exists resp. check_type_size instead

Solution: Group include directives together at the beginning of the CMakeLists.txt file

Solution: remove it

Solution: fix spelling

Solution: remove redundant debug output

Fix a typo in root CMakeLists.txt

Problem: build broken on Fedora 30

Solution: use AC_COMPILE_IFELSE instead of AC_CHECK_FUNCS to check for
strnlen, as the latter does not work anymore.

Problem: Missing doc & unit tests for zmq_poller_fd

Solution: Add some and document it.

Solution: Add doc & unit tests

Problem: zmq_socket_monitor example did not include HANDSHAKE_SUCCEEDED event causing assert failure

 Problem: Cannot get thread safe socket fd 

Solution: add one

Solution: Add a method to get the zmq_poller's signaler fd. Then we can
associate a poller instance with every thread safe socket and use its
fd.

Problem: unused Windows-specific code in sleep_ms

Solution: remove it since sleep_ms isn't used on Windows

Add <ios> include to fix uClibc++ compilation

Signed-off-by: Rosen Penev <rosenp@gmail.com>

Under uClibc++, streamoff is defined in <ios>. This header is needed to fix compilation.

Zeromq 3479: fixed build for QNX 6.6 with CMake

Solution: Use a toolchain file for QNX x86

Solution: added relicense agreement

Solution: libm and libsocket have to be linked explicitely

Fix Radix Tree benchmark includes when used as submodule

Solution: Add a relicense statement for Omegastick

Solution: Use CMAKE_CURRENT_LIST_DIR instead of CMAKE_SOURCE_DIR when findng includes

Problems: formatting errors in docs reported by linters

Solution: fix it