CMakeLists.txt:
  Moved zlib to be processed before extra as CMake doesn't handle
  forward references well.
client/CMakeLists.txt:
  Ensure that -DTHREADS is specified for mysqlslap.c
client/mysqlslap.c:
  Removed includes which are already included in client_priv.h
  Moved variable declarations to be at start of function before any
  code is emitted as VSC is strict.