Fix CMakeLists.txt for cmake Ninja generator
remove HTON_FLUSH_AFTER_RENAME (BDB-ism, unused for years)
MDEV-4260 Don't create frm files for temporary tables

* Don't write frm for tmp tables
* pass frm image down to open_table_uncached, when possible
* don't use truncate-by-recreate for temp tables - cannot recreate
  without frm, and delete_all_rows is faster anyway