MDEV-10214: Fix segfault when using groups in PAM user mapping plugin

MDEV-8686 A user defined collation utf8_confusables doesn't work
25e68c5e

The collation customization code for the UCA (Unicode Collation Alrorithm)
based collations now allows to reset to and shift of characters with
implicit weights. Previously reset/shift worked only for the characters
with explicit DUCET weights. An attempt to use reset/shift with
character with implicit weights made the server crash.

Make tree_or set correct SEL_TREE::keys_map for the result.

Fixed mysql-test-run failures for roles.acl_statistics

The check inserts a DWARF directive to tell stack unwinding that the
bottom of the (co-routine) stack has been reached. Without this, stack
traces may attempt to continue past the bottom of the stack.

The GCC version check was incorrect, and failed to trigger for GCC
version 5.[0123].

On Windows with low precision  (10-16 ms) timer used for timing queries,
the statement "set @@long_query_time=0.01" can log itself a slow if it
spawn more single timer tick.

The fix is to filter this query out  from "SELECT FROM mysql.slow_log"
results

Make the range optimizer not call records_in_range() when it would
not give any benefit.

Part #2: make tree_or(tree1, tree2) to reuse tree1 for the result object
for simple cases. These include key IN (c1, ... cN).

The reuse was happening in old MySQL versions, but we stopped doing it
in the "fair choice between range and index_merge" patch.

MDEV-10154 - Remove some unnecessary parentheses

Post-fix #2:
- Update test results
- Make the optimization conditional under @@optimizer_switch flag.
- The optimization is now disabled by default, so .result files
  are changed back to be what they were before the MDEV-8989 patch.

Add big_test and not_debug requirements to avoid timeouts.

Fix spelling: shhould -> should

A partial backport of 67f21fb3a077dedfd14b9ca720e926c55e682f93,
Bug#22283790: RANGE OPTIMIZER UTILIZES TOO MUCH MEMORY WITH MANY OR CONDITIONS

The backported part changes SEL_TREE::keys from being an array of
MAX_KEY elements (64*8=512 bytes) to a Mem_root_array<SEL_ARG*> (32 bytes +
alloc'ed array of as many elements as we need).

The patch doesn't fix the "not limiting memory" part, but the memory usage
is much lower with it.

utf8mb4_thai_520_w2, ucs2_thai_520_w2, utf16_thai_520_w2, utf32_thai_520_w2

  from ctype_uca.test. This is to reuse ctype_thai.inc for other Unicode
  character sets later
- Removing separate ctype_uca.result

  and including it from t/ctype_uca.test
- Deleting r/ctype_uca_th.result

They have bytes 0x25 and 0x5F. Testing that these bytes are treated as parts
of multi-byte characters rather than underscore and percent sign.

Mark gssapi plugin as stable. No open bug reports, and no further work planned, thus stable is accurate

Post-fix: add comments, remove dead-code.

- Changing strnxfrm_multiply from 8 to 4, as agreed with Pruet Boonma
- Adjusting tests

Variant #4 of the fix.

Make ORDER BY optimization functions take into account multiple
equalities. This is done in several places:
- remove_const() checks whether we can sort the first table in the
  join, or we need to put rows into temp.table and then sort.
- test_if_order_by_key() checks whether there are indexes that
  can be used to produce the required ordering
- make_unireg_sortorder() constructs sort criteria for filesort.

When simplify_joins() converts an outer join to an inner, it should
reset the value of TABLE::dep_tables.  This is needed, because the
function may have already set TABLE::dep_tables according to the outer
join dependency.