POCO maps Emscripten to POCO_OS_LINUX (Foundation/include/Poco/Platform.h), so
Net.h would define POCO_HAVE_FD_EPOLL there, but Emscripten has no <sys/epoll.h>.
Exclude Emscripten so PollSet/SocketImpl fall back to their select()-based
implementation (the same approach as the older wasm/poco-*-emscripten.patch).

--- a/Net/include/Poco/Net/Net.h
+++ b/Net/include/Poco/Net/Net.h
@@ -137,7 +137,7 @@
 #endif
 
 
-#if (POCO_OS == POCO_OS_LINUX) || (POCO_OS == POCO_OS_WINDOWS_NT) || (POCO_OS == POCO_OS_ANDROID)
+#if ((POCO_OS == POCO_OS_LINUX) || (POCO_OS == POCO_OS_WINDOWS_NT) || (POCO_OS == POCO_OS_ANDROID)) && !defined(POCO_EMSCRIPTEN)
 	#define POCO_HAVE_FD_EPOLL 1
 #endif