MDEV-22217 Make OS character sets "utf8" and "utf-8" map to MariaDB character set "utf8mb4"

Map Unix utf8 locales to utf8mb4 instead of utf8mb3.

Author: abarkov

mysql-test/main/mysql_locale_posix.result

@@ -33,7 +33,7 @@ Database: ó
 
 utf8
 @@character_set_client
-utf8mb3
+utf8mb4
 Database: ó
 +--------+
 | Tables |
@@ -70,3 +70,16 @@ DROP DATABASE `ó`;
 DROP DATABASE `Ăł`;
 DROP DATABASE `цЁ`;
 DROP DATABASE `ó`;
+#
+# Start of 11.8 tests
+#
+#
+# MDEV-22217 Make OS character sets "utf8" and "utf-8" map to MariaDB character set "utf8mb4"
+#
+VARIABLE_NAME	VARIABLE_VALUE
+CHARACTER_SET_CLIENT	utf8mb4
+CHARACTER_SET_CONNECTION	utf8mb4
+CHARACTER_SET_RESULTS	utf8mb4
+#
+# End of 11.8 tests
+#

mysql-test/main/mysql_locale_posix.test

@@ -203,3 +203,17 @@ DROP DATABASE `ó`;
 DROP DATABASE `Ăł`;
 DROP DATABASE `цЁ`;
 DROP DATABASE `ó`;
+
+--echo #
+--echo # Start of 11.8 tests
+--echo #
+
+--echo #
+--echo # MDEV-22217 Make OS character sets "utf8" and "utf-8" map to MariaDB character set "utf8mb4"
+--echo #
+
+--exec LC_ALL=en_US.utf8 $MYSQL --default-character-set=auto test -e "select * from information_schema.session_variables where variable_name rlike 'character_set_(connection|client|results)' order by variable_name"
+
+--echo #
+--echo # End of 11.8 tests
+--echo #

mysys/charset.c

@@ -1564,8 +1564,8 @@ static const MY_CSET_OS_NAME charsets[] =
 
   {"US-ASCII",       "latin1",   my_cs_approx},
 
-  {"utf8",           "utf8",     my_cs_exact},
-  {"utf-8",          "utf8",     my_cs_exact},
+  {"utf8",           "utf8mb4",  my_cs_exact},
+  {"utf-8",          "utf8mb4",  my_cs_exact},
 #endif
   {NULL,             NULL,       0}
 };