cmake HAVE_SYM_DEF examples

fluffos/fluffos src/thirdparty/libevent/cmake/Macros.cmake :18 

CHECK_SYMBOL_EXISTS(${SYMNAME} "${HEADERS}" ${HAVE_SYM_DEF})

CTSRD-CHERI/cheribsd contrib/libevent/cmake/Macros.cmake :18 

CHECK_SYMBOL_EXISTS(${SYMNAME} "${HEADERS}" ${HAVE_SYM_DEF})

CTSRD-CHERI/cheribsd contrib/ntp/sntp/libevent/cmake/Macros.cmake :18 

CHECK_SYMBOL_EXISTS(${SYMNAME} "${HEADERS}" ${HAVE_SYM_DEF})