cmake HAVE_SIGEMPTYSET examples

arkdb/inception configure.cmake :471 

CHECK_FUNCTION_EXISTS (sigemptyset HAVE_SIGEMPTYSET)

alibaba/AliSQL configure.cmake :578 

CHECK_FUNCTION_EXISTS (sigemptyset HAVE_SIGEMPTYSET)

Tokutek/mysql-5.5 configure.cmake :411 

CHECK_FUNCTION_EXISTS (sigemptyset HAVE_SIGEMPTYSET)