[cmake] help cmake on FreeBSD find sys/event.h

sys/event.h does not compile standalone, so check_include_files() fails

Add compiler flags -include sys/types.h so that the compile check passes

This allows cmake builds on FreeBSD to detect and use kqueue.

src/CMakeLists.txt

@@ -78,7 +78,9 @@ endif()
 
 check_include_files(sys/devpoll.h HAVE_SYS_DEVPOLL_H)
 check_include_files(sys/epoll.h HAVE_SYS_EPOLL_H)
+set(CMAKE_REQUIRED_FLAGS "-include sys/types.h")
 check_include_files(sys/event.h HAVE_SYS_EVENT_H)
+set(CMAKE_REQUIRED_FLAGS)
 check_include_files(sys/mman.h HAVE_SYS_MMAN_H)
 check_include_files(sys/poll.h HAVE_SYS_POLL_H)
 check_include_files(sys/port.h HAVE_SYS_PORT_H)