[core] Set CLOEXEC for epoll on Linux

epoll_create1() was added to the kernel in version 2.6.27. Library
support is provided in glibc starting with version 2.9 which was
released at the year of 2008.

srtcore/epoll.cpp

@@ -108,7 +108,11 @@ int CEPoll::create(CEPollDesc** pout)
    int localid = 0;
 
    #ifdef LINUX
-   localid = epoll_create(1024);
+   int flags = 0;
+#if ENABLE_SOCK_CLOEXEC
+   flags |= EPOLL_CLOEXEC;
+#endif
+   localid = epoll_create1(flags);
    /* Possible reasons of -1 error:
 EMFILE: The per-user limit on the number of epoll instances imposed by /proc/sys/fs/epoll/max_user_instances was encountered.
 ENFILE: The system limit on the total number of open files has been reached.