Documentation fixes

MDEV-9354: Debian: unmask the mysql.service on installation

MDEV-9433: mysys/my_rnd.c - remove #ifdef __cplusplus

MDEV-9471: Server crashes or returns an error while trying to alter partitioning on a table moved from Windows to Linux

At alter table when server renames the table to temporal name,
old name uses normal partioned table naming rules. However,
if tables are created on Windows and then transfered to Linux
and lower-case-table-names=1 we should modify the old name
on rename to lower case to be able to find it from the
InnoDB dictionary.

create_partition_index_description() had wrong logic to calculate
length of the key value buffer that is used by the range optimizer.

For some reason it used MAX(partitioning_columns_len,
subpartitioning_columns_len) while it should use SUM of these values.

Conflicts:
	configure.cmake

The check for UCONTEXT in cmake was somehow become broken, disabling the
fallback to ucontext. This caused the non-blocking client API to not be
available for non-x86 platforms, on which no hand-crafted assembler
implementation of my_context is available.

  Change parser so it saves all the query line to the ';' in the
    sp_instr::m_query.

Conflicts:
	plugin/server_audit/server_audit.c

Conflicts:
	sql/slave.cc

This occurs when replication stops with an error, domain-based parallel
replication is used, and the GTID position contains more than one domain.
Furthermore, it relates to the case where the SQL thread is restarted
without first stopping the IO thread.

In this case, the file/offset relay-log position does not correctly
represent the slave's multi-dimensional position, because other domains may
be far ahead of, or behind, the domain with the failing event. So the code
reverts the relay log position back to the start of a relay log file that is
known to be before all active domains.

There was a bug that when the SQL thread was restarted, the
rli->relay_log_state was incorrectly initialised from @@gtid_slave_pos. This
position will likely be too far ahead, due to reverting the relay log
position. Thus, if the replication fails again after the SQL thread restart,
the rli->restart_gtid_pos might be updated incorrectly. This in turn would
cause a second SQL thread restart to replicate from the wrong position, if
the IO thread was still left running.

The fix is to initialise rli->relay_log_state from @@gtid_slave_pos only
when we actually purge and re-fetch relay logs from the master, not at every
SQL thread start.

A related problem is the use of sql_slave_skip_counter to resolve
replication failures in this kind of scenario. Since the slave position is
multi-dimensional, sql_slave_skip_counter can not work properly - it is
indeterminate exactly which event is to be skipped, and is unlikely to work
as expected for the user. So make this an error in the case where
domain-based parallel replication is used with multiple domains, suggesting
instead the user to set @@gtid_slave_pos to reliably skip the desired event.

        fixing Windows crash.

   updata thread_pool_server_audit test result.

    MariaDB 5.5 built in debug gets unhappy with mutexes.
    Although everything is correct, some DBUG_ASSERT can happen.
    So this patch keeps safe_mutex silent.

        The audit API was seriously changed in MySQL 5.7.
        so we had to adapt the plugin's code to that.

Unmask the systemd mysql.service if left behind by mysql-server-5.6

Without this a simple 'apt-get install mariadb-server' would end
up with a system where mysqld is not running despite it was
running OK with mysql-server-5.6 installed, and users might wrongly
think mariadb-server package is broken when the real cause was
the removal of mysql-server-5.6 that left a /etc/systemd/system/
file behind pointing to /dev/null.

Fix test whether process is alive in mysqltest.

Also fix SHUT_RD definition on Windows to be SD_RECEIVE.
SD_BOTH  was used instead prior to this patch, and this would
occasionally make mysql_shutdown()  fail - when the socket for the current connection
is not able send the COM_SHUTDOWN response anymore.

If GCC or CLang compile with link time optimization (-flto),
they throw an error during link , when lto sees a
function (e.g mysql_real_connect) is redeclared as "external void *"
in libmysql_exports.cc

The fix disables -flto for generated libmysql_exports.cc

The problem was that wait_for_slave_io_to_start reported that the io thread
was ready, when it was still initializing. This caused test suite to
continue too early, for example before the semi sync plugin was properly
enabled.

Fixed by introducing a new internal stage: "Preparing". Slave_IO_Running is
now set to "Yes" only when all initializing is done and the IO thread is
ready to read things from the master.

The only test affected by this change is rpl_flsh_tbls, which got stuck in
the preparing phase while trying to read the GTID position from a table.
Fixed by having this test waiting for Preparing instead of Yes.

- Added testing if connection is killed to shortcut reading of connection data
  This will allow us later in 10.2 to do a cleaner shutdown of slaves (less errors in the log)
- Add new status variables: Slaves_connected, Slaves_running and Slave_connections.
- Use MYSQL_SLAVE_NOT_RUN instead of 0 with slave_running.
- Don't print obvious extra warnings to the error log when slave is shut down normally.

Fixed compiler warnings
Added --big-test to tokudb change_column_char & change_column_bin

Fix process  handle leak in buildbot. GenerateConsoleCtrlEvent sent to non-existing process will add a process handle to this non-existing process to console host process conhost.exe

as it's needed for Cassandra in 10.0.

Provided IBM System Z have outdated compiler version, which supports gcc sync
builtins but not gcc atomic builtins. It also has weak memory model.

InnoDB attempted to verify if __sync_lock_test_and_set() is available by
checking IB_STRONG_MEMORY_MODEL. This macro has nothing to do with availability
of __sync_lock_test_and_set(), the right one is HAVE_ATOMIC_BUILTINS.

Provided IBM System Z have outdated compiler version, which supports gcc sync
builtins but not gcc atomic builtins. It also has weak memory model.

InnoDB attempted to verify if __sync_lock_test_and_set() is available by
checking IB_STRONG_MEMORY_MODEL. This macro has nothing to do with availability
of __sync_lock_test_and_set(), the right one is HAVE_ATOMIC_BUILTINS.