Patch 3: Adapt to MySQL build system.

For bundled libevent, do not use the obsolete libevent library,
use event_core event_extra event_openssl

Changes to libevent CMakeLists.txt
 - Disable default build type Release.
 - Disable default cmake configuration types.
 - Bug#29226065 SILENCE 3RD PARTY CODE COMPILATION WARNINGS
 - Use CMAKE_PUSH_CHECK_STATE / CMAKE_POP_CHECK_STATE
 - Bug #31109804 THE HEADER <SYS/SYSCTL.H> IS DEPRECATED
 - Disable arc4random_addrandom
 - Disable find_package(OpenSSL REQUIRED), this is done in our ssl.cmake
 - Disable find_package(ZLIB), only relevant for libevent unit testing.
 - BUG 29552366:LIBEVENT PRODUCES A LOT OF "'WIN32_LEAN_AND_MEAN': MACRO REDEFINITION" ON WIN32
 - Add library dependencies event_extra -> event_core and event_openssl -> event_core
   (those missing dependencies seems to be a bug in the bundled CMakeLists.txt)
 - Add RETURN() to skip generation of all the internal things we do not need.

   Extra changes for 5.7:
   - Ensure that we build with -fPIC
   - INCLUDE_DIRECTORIES(BEFORE SYSTEM ${SSL_INCLUDE_DIRS})
   - Lower the cmake_minimum_required VERSION to what we actually use in 5.7
     The requirement for 3.1 seems to be for find_package(OpenSSL),
     which we do not use anyways.

Changes to libevent VersionViaGit.cmake
 - Remove code asking git about what version we are at.
   We know the bundled version is 2.1.11.stable so don't ask *our* git repo.

Changes to libevent util-internal.h
 - Disable EVUTIL_HAS_ATTRIBUTE for Oracle Developer Studio,
   it gives compiler errors.

Change-Id: I201a855305136d166c1ba12336ec84e7fea4c8b8
(cherry picked from commit 3486fca7dfb35954c05841657bf4913b31452f14)
(cherry picked from commit c309ad9e8e95c7bd20fadc8d32d436a8269d06ce)