MariaDB doesn't support Read-Free replication, so showing them only causes
confusion.
Removed variables:
- @@rocksdb_read_free_rpl
- @@rocksdb_read_free_rpl_tables

The test cases for the MDEV found several independent bugs
in MariaDB server and Aria:
- If a temporary table was marked as crashed, it could never
  be deleted.
- Opening of a crashed temporary table gave an error message
  but the error was never forwarded to the caller which caused
  an assert() in my_ok()
- init_read_record() did mmap of all temporary tables, which is
  probably not a good idea as this area can potentially be
  very big. Changed code to only mmap internal temporary tables.
- mmap-ed tables where not unmapped in case of repair/optimize
  which caused bad data in table and crashes if the original
  table files where replaced with new ones (as the old mmap
  was still in place). Fixed by removing the mmap in case
  of repair.
- Cleaned up usage of code that disabled mmap in Aria

Problem was that in case of implicit rollback for alter table
Aria did try to run commit twice.

The test case for this is tricky to do in 10.2, so it will
be added to 10.4 as part of BACKUP STAGE testing.

Do not check my_errno before it is set, check errno instead.
Also, do not check errno, if prior pread() did not fail.

Restore the detection of default charset in command line utilities.
It worked up to 10.1, but was broken by Connector/C.

Moved code for detection of default charset from sql-common/client.c
to mysys, and make command line utilities to use this code if charset
was not specified on the command line.

There was two separate problems:
- Aria pagecache didn't properly handle re-reading of blocks
  that have given errors before (this triggered an assert)
- temporary tables that where opened several times where
  not properly closed in ALTER, REPAIR or OPTIMIZE table

Other things
- Added a couple of asserts that will make it easier to
  find problems like this in the future.

- Don't add DZSTD_STATIC_LINKING_ONLY
- Don't use upstream's way of linking with Jemalloc (MyRocks/MariaDB has
  its own in build_rocksdb.cmake)
- Don't depend on libunwind

MariaDB generates both errors and warnings. Warnings are not normally
visible when errors are also produced.

Avoid unnecessary creation of named objects for invoking
mtr_buf_t::for_each_block_in_reverse().

    Copy of
    commit dcd9379eb5707bc7514a2ff4d9127790356505cb
    Author: Manuel Ung <mung@fb.com>
    Date:   Fri Jun 14 10:38:17 2019 -0700

        Skip valgrind for rocksdb.force_shutdown

        Summary:
        This test does unclean shutdown, and leaks memory.

        Squash with: D15749084

        Reviewed By: hermanlee

        Differential Revision: D15828957

        fbshipit-source-id: 30541455d74

commit dcd9379eb5707bc7514a2ff4d9127790356505cb
Author: Manuel Ung <mung@fb.com>
Date:   Fri Jun 14 10:38:17 2019 -0700

    Skip valgrind for rocksdb.force_shutdown

    Summary:
    This test does unclean shutdown, and leaks memory.

    Squash with: D15749084

    Reviewed By: hermanlee

    Differential Revision: D15828957

    fbshipit-source-id: 30541455d74

Fixes also MDEV-17837

Problem was that we did not ignore warnings from virtual fields when
updated virtual fields for to-be-replaced row.

when copying the TREE, take into account that init_tree can
internally adjust tree->size_of_element

Problem:
=========
One of the purge thread access the corrupted page and tries to remove from
LRU list. In the mean time, other purge threads are waiting for same page
in buf_wait_for_read(). Assertion(buf_fix_count == 0) fails for the
purge thread which tries to remove the page from LRU list.

Solution:
========
- Set the page id as FIL_NULL to indicate the page is corrupted before
removing the block from LRU list. Acquire hash lock for the particular
page id and wait for the other threads to release buf_fix_count
for the block.

- Added the error check for btr_cur_open() in row_search_on_row_ref().