MDEV-34388 default stack size under MSAN needs increasing

Without this increase the mtr test case pre/post conditions will
fail as the stack usage has increased under MSAN with clang-20.1.

ASAN takes a 11M stack, however there was no obvious gain in MSAN
test success after 2M.

The resulting behaviour observed on smaller stack size was a
SEGV normally.

Hide the default stack size from the sysvar tests that expose
thread-stack as a variable with its default value.

include/my_pthread.h

@@ -668,7 +668,17 @@ extern void my_mutex_end(void);
   We need to have at least 256K stack to handle calls to myisamchk_init()
   with the current number of keys and key parts.
 */
-# if defined(__SANITIZE_ADDRESS__) || defined(WITH_UBSAN)
+#if !defined(__has_feature)
+#define __has_feature(x) 0
+#endif
+#if defined(__clang__) && __has_feature(memory_sanitizer) && !defined(DBUG_OFF)
+/*
+  MSAN in Debug with clang-20.1 required more memory to complete
+  mtr begin/end checks. The result without increase was MSAN
+  errors triggered on a call instruction.
+*/
+#  define DEFAULT_THREAD_STACK	(2L<<20)
+# elif defined(__SANITIZE_ADDRESS__) || defined(WITH_UBSAN)
 /*
   Optimized WITH_ASAN=ON executables produced
   by GCC 12.3.0, GCC 13.2.0, or clang 16.0.6

mysql-test/main/mysqld--help.result

@@ -1891,7 +1891,6 @@ thread-pool-oversubscribe 3
 thread-pool-prio-kickup-timer 1000
 thread-pool-priority auto
 thread-pool-stall-limit 500
-thread-stack 299008
 time-format %H:%i:%s
 tmp-disk-table-size 18446744073709551615
 tmp-memory-table-size 16777216

mysql-test/main/mysqld--help.test

@@ -27,7 +27,7 @@ perl;
                large-files-support lower-case-file-system system-time-zone
                collation-server character-set-server log-tc-size table-cache
                table-open-cache table-open-cache-instances max-connections
-               server-uid tls-version version.* analyze-max-length/;
+               server-uid tls-version version.* analyze-max-length thread-stack/;
 
   # Plugins which may or may not be there:
   @plugins=qw/innodb archive blackhole federated partition s3

mysql-test/suite/sys_vars/t/thread_stack_basic.test

@@ -3,6 +3,7 @@
 #
 --source include/not_asan.inc
 --source include/not_ubsan.inc
+--source include/not_msan.inc
 --replace_result 392192 299008
 select @@global.thread_stack;
 --error ER_INCORRECT_GLOBAL_LOCAL_VAR