Remove the following unused #ifdefs:
  CANT_DELETE_OPEN_FILES
  CHECK_EMBEDDED_DIFFERENCES
  MY_ATOMIC_HAS_8_16
  NEED_SYS_SYSLOG_H
  NO_CLIENT_LONG_LONG
  NO_STRTOLL_PROTO
  OLD_HEAP_VERSION
  OLD_VERSION
  SHARED_LIBRARY
  SSL_VARS_NOT_STATIC
  USE_MY_STAT_STRUCT
  USE_OLD_FUNCTIONS
  USE_SYSTEM_WRAPPERS
  WANT_OLD_HEAP_VERSION

Also remove the remaining support for Borland C.