Problem: no CI build on Windows with POLLER=poll

Solution: add appveyor job

appveyor.yml

@@ -51,6 +51,15 @@ environment:
       CMAKE_GENERATOR: "Visual Studio 15 2017"
       MSVCVERSION: "v141"
       MSVCYEAR: "vs2017"
+    - platform: Win32
+      configuration: Release
+      POLLER: poll
+      WITH_LIBSODIUM: ON
+      ENABLE_CURVE: ON
+      APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
+      CMAKE_GENERATOR: "Visual Studio 15 2017"
+      MSVCVERSION: "v141"
+      MSVCYEAR: "vs2017"
 
 matrix:
   fast_finish: false
@@ -78,7 +87,7 @@ before_build:
   - cmd: set LIBZMQ_BUILDDIR=C:\projects\build_libzmq
   - cmd: md "%LIBZMQ_BUILDDIR%"
   - cd "%LIBZMQ_BUILDDIR%"
-  - cmd: cmake -D CMAKE_INCLUDE_PATH="%SODIUM_INCLUDE_DIR%" -D CMAKE_LIBRARY_PATH="%SODIUM_LIBRARY_DIR%" -D WITH_LIBSODIUM="%WITH_LIBSODIUM%" -D ENABLE_CURVE="%ENABLE_CURVE%" -D CMAKE_C_FLAGS_RELEASE="/MT" -D CMAKE_C_FLAGS_DEBUG="/MTd" -D WITH_LIBSODIUM="%WITH_LIBSODIUM%" -G "%CMAKE_GENERATOR%" "%APPVEYOR_BUILD_FOLDER%"
+  - cmd: cmake -D CMAKE_INCLUDE_PATH="%SODIUM_INCLUDE_DIR%" -D CMAKE_LIBRARY_PATH="%SODIUM_LIBRARY_DIR%" -D WITH_LIBSODIUM="%WITH_LIBSODIUM%" -D ENABLE_CURVE="%ENABLE_CURVE%" -D POLLER="%POLLER%" -D CMAKE_C_FLAGS_RELEASE="/MT" -D CMAKE_C_FLAGS_DEBUG="/MTd" -D WITH_LIBSODIUM="%WITH_LIBSODIUM%" -G "%CMAKE_GENERATOR%" "%APPVEYOR_BUILD_FOLDER%"
 
 build:
   parallel: true