cmake EVENT__HAVE_PTHREADS examples

fluffos/fluffos src/thirdparty/libevent/CMakeLists.txt :1293 

elseif (EVENT__HAVE_PTHREADS)

CTSRD-CHERI/cheribsd contrib/libevent/CMakeLists.txt :1133 

elseif (EVENT__HAVE_PTHREADS)

CTSRD-CHERI/cheribsd contrib/ntp/sntp/libevent/CMakeLists.txt :1133 

elseif (EVENT__HAVE_PTHREADS)