cmake Libevent2 examples

mysql/mysql-router CMakeLists.txt :62 

find_package(LibEvent2 2.0 MODULE REQUIRED)

sems-server/sems CMakeLists.txt :105 

FIND_PACKAGE(Libevent2 REQUIRED)

chux0519/pegasocks CMakeLists.txt :118 

find_package(Libevent2 REQUIRED)