myrg_open(): Reduce the scope of the variable 'end' and
simplify the code.

For some reason, I got no warning for this code in the 10.2
branch, only 10.3 or later.

The ENGINE=MERGE is covered by the tests main.merge, main.merge_debug,
and main.merge-big.

Problem:
=======
When we upgrade from "mysql" to "mariadb" if slave is using repositories as
tables their data is completely ignored and no warning is issued in error log.

Fix:
===
"mysql_upgrade" test should check for the presence of data in
"mysql.slave_master_info" and "mysql.slave_relay_log_info" tables. When tables
have some data the upgrade script should report a warning which hints users
that the data in repository tables will be ignored.

_ma_fetch_keypage(): Correct an assertion that used to always hold.
Thanks to clang -Wint-in-bool-context for flagging this.

double_to_datetime_with_warn(): Suppress -Wimplicit-int-float-conversion
by adding a cast. LONGLONG_MAX converted to double will actually be
LONGLONG_MAX+1.

All tablespace metadata is buffered in fil_system. There is a LRU
mechanism, but that only controls the opening and closing of
fil_node_t::handle.

It is much more efficient and less error-prone to access data file names
by looking up the fil_space_t object rather than by essentially joining
each row with an access to SYS_DATAFILES via the InnoDB internal SQL parser.

dict_get_first_path(): Declare static. The function may only be needed
when loading or updating the data dictionary. Also, change a condition
in order to avoid a bogus GCC 10 -Wstringop-overflow warning for
mem_strdupl() about len==ULINT_UNDEFINED.

i_s_sys_tablespaces_fill_table(): Do not access other InnoDB internal
dictionary tables than SYS_TABLESPACES.

This fixes GCC 10.0.1 -Wstringop-truncation and some typos.

actually, page_zip_verify_checksum() generally allows all-zeroes
checksums because our CRC32 checksum is something like
crc_1 ^ crc_2 ^ crc_3

Also, all zeroes page is considered correct.

As a side effect fix nasty reinterpret_cast<> UB

Also, since c0f47a4a innodb_checksum_algorithm=full_crc32
exists which computes CRC32 in one go (without bitwise arithmetic)

Also, remove some trailing white space and add missing static
qualifier to free_annotate_event().

It was:
implicit conversion from 'ha_rows' (aka 'unsigned long long') to 'double'
changes value from 18446744073709551615 to 18446744073709551616

Follow what JOIN::get_examined_rows() does for similar code.

Parser: uninitialized Lex->create_last_non_select_table under
mysql_unpack_partition() fix.

Tested with main, parts suites.

Re-enable main.mysql_client_test on all builders, because
at the moment we do not run any --big-test on buildbot
due to resource constraints.

A number of tests were declared big in
commit eeee1832
in an attempt to save resources on buildbot.

The default keyread_time() was optimized for blocks and not suitable for
HEAP. The effect was the HEAP prefered table scans over ranges for btree
indexes.
Fixed also get_sweep_read_cost() for HEAP tables.

- Move testing of my_writer to inline functions to avoid calls
- Made more functions inline. Especially thd->thread_started()
  is now very optimized!
- Moved Opt_trace_stmt classe to opt_trace_context.h to get critical
  functions inline

- Added unlikely() to optimize for not having optimizer trace enabled
- Made THD::trace_started() inline
- Added 'if (trace_enabled())' around some potentially expensive code
  (not many found)
- Added ASSERT's to ensure we don't call expensive optimizer trace calls
  if optimizer trace is not enabled
- Added length to Json_writer functions to speed up buffer writes
  when optimizer trace is enabled.
- Changed LEX_CSTRING argument handling to not send full struct to writer
  function on_add_str() functions now trusts length arguments

Stop masking the Data_free values, because innodb_file_per_table=1
is the default.

Also, do mask Update_time after updating tables, even though for
some reason it does appear to matter.

Change events only on Galera environment where idea is that
event is enabled only on one node of the cluster and nodes
are identified by server_id.

* Small refactor of my_getncpus function to compile for very old glibc < 2.6.
* Cleanup code to eliminate duplication.