build: default to epoll for MinGW on Windows (fix IPC/select issue)

MinGW builds were falling back to select poller, which is incompatible with IPC
and causes compilation failure.
Default epoll is now enabled for both MSVC and MinGW to ensure consistent behavior.
Comments updated accordingly.

Author: ynkan

CMakeLists.txt

@@ -383,13 +383,14 @@ if(WIN32)
       "${ZMQ_WIN32_WINNT_DEFAULT}"
       CACHE STRING "Value to set _WIN32_WINNT to for building [default=autodetect from build environment]")
 
-  # On Windows Vista or greater, with MSVC 2013 or greater, default to epoll (which is required on Win 10 for ipc
-  # support)
+  # On Windows Vista or greater, default to epoll for MSVC 2013+ and MinGW
+  # to avoid falling back to select, which is incompatible with IPC transport.
   if(ZMQ_WIN32_WINNT GREATER "0x05FF"
-     AND MSVC_VERSION GREATER 1799
      AND POLLER STREQUAL ""
      AND NOT ZMQ_HAVE_WINDOWS_UWP)
-    set(POLLER "epoll")
+    if(MSVC_VERSION GREATER 1799 OR MINGW)
+      set(POLLER "epoll")
+    endif()
   endif()
 
   add_definitions(-D_WIN32_WINNT=${ZMQ_WIN32_WINNT})