Problem: no CI with VS2019 or any VS with C++11/14/17 mode, build broken in C++17 mode

Solution: add CI configuration and fix active_poller.cpp

appveyor.yml

@@ -1,6 +1,7 @@
 version: build-{build}
 
 os:
+    - Visual Studio 2019
     - Visual Studio 2017
     - Visual Studio 2015
 

tests/CMakeLists.txt

@@ -29,8 +29,12 @@ add_executable(
     send_multipart.cpp
     monitor.cpp
     utilities.cpp
+    ../zmq.hpp
+    ../zmq_addon.hpp
 )
 
+set_property(TARGET unit_tests PROPERTY CXX_STANDARD 17)
+
 add_dependencies(unit_tests catch)
 
 target_include_directories(unit_tests PUBLIC ${CATCH_MODULE_PATH})

tests/active_poller.cpp

@@ -158,6 +158,8 @@ namespace
 {
 struct server_client_setup : common_server_client_setup
 {
+    using common_server_client_setup::common_server_client_setup;
+
     zmq::active_poller_t::handler_type handler = [&](zmq::event_flags e)
     {
         events = e;

zmq.hpp

@@ -33,13 +33,15 @@
 #endif
 #if (defined(__cplusplus) && __cplusplus >= 201402L)                                \
   || (defined(_HAS_CXX14) && _HAS_CXX14 == 1)                                       \
-  || (defined(_HAS_CXX17)                                                           \
-      && _HAS_CXX17                                                                 \
-           == 1) // _HAS_CXX14 might not be defined when using C++17 on MSVC
+  || (defined(_HAS_CXX17) && _HAS_CXX17 == 1)                                       \
+  || (defined(_MSVC_LANG)                                                           \
+      && _MSVC_LANG                                                                 \
+           >= 201402L) // _HAS_CXX14 might not be defined when using C++17 on MSVC
 #define ZMQ_CPP14
 #endif
 #if (defined(__cplusplus) && __cplusplus >= 201703L)                                \
-  || (defined(_HAS_CXX17) && _HAS_CXX17 == 1)
+  || (defined(_HAS_CXX17) && _HAS_CXX17 == 1)                                       \
+  || (defined(_MSVC_LANG) && _MSVC_LANG >= 201703L)
 #define ZMQ_CPP17
 #endif