A follow-up for WL#5624: Collation customization improvements

The reasons for failures to initialize a user collation defined
in Index.xml are now correctly reported                                  
(in SHOW WARNINGS and in the server error log) if the COLLATE clause
is used with an expression, e.g.:

  SELECT <exrp> COLLATE <collation name> FROM t1;

Previously, the failure reasons were reported only by COLLATE clauses
in SET NAMES and in DDL statements, e.g.:

  SET NAMES utf8 COLLATE utf8_xxx_ci;
  CREATE TABLE t1 (a VARCHAR(1) CHARACTER SET utf8 COLLATE utf8_xxx_ci);

mysql-test/t/ctype_ldml.test

@@ -249,6 +249,10 @@ DROP TABLE t1;
 SET NAMES utf8 COLLATE utf8_5624_2;
 SHOW WARNINGS;
 
+--error ER_UNKNOWN_COLLATION
+SELECT _utf8'test' COLLATE utf8_5624_2;
+SHOW WARNINGS;
+
 --echo #
 --echo # WL#5624, reset before primary ignorable
 --echo #
@@ -353,7 +357,7 @@ DROP TABLE t1;
 --let $out_file= $MYSQLTEST_VARDIR/tmp/ctype_ldml_log.err
 --let OUTF= $out_file
 # Error messages are not seen in error log in embedded version
---let EMBEDDED=`SELECT version() LIKE '%embedded%'`
+--let EMBEDDED=`SELECT IF(version() LIKE '%embedded%',2,0)`
 --echo # Search for occurrences of [ERROR] Syntax error at '[strength tertiary]'
 
 perl;

sql/item_strfunc.cc

@@ -3463,11 +3463,8 @@ void Item_func_set_collation::fix_length_and_dec()
 					 MY_CS_BINSORT,MYF(0));
   else
   {
-    if (!(set_collation= get_charset_by_name(colname,MYF(0))))
-    {
-      my_error(ER_UNKNOWN_COLLATION, MYF(0), colname);
+    if (!(set_collation= mysqld_collation_get_by_name(colname)))  
       return;
-    }
   }
 
   if (!set_collation ||