Bug#39972 mysql-test-run.pl: Confusing error message under special conditions

 - Fix problem with for example ./mtr --timer, caused by new version of "Getopt::Long"
 - Evaluating the "$opt" variable as a string, returns the name of the parameter
   to be modified instead of "Getopt::Long::Callback" which is the class name

mysql-test/lib/mtr_cases.pm

@@ -45,10 +45,13 @@ our $reorder= 1;
 sub collect_option {
   my ($opt, $value)= @_;
 
+  # Evaluate $opt as string to use "Getopt::Long::Callback legacy API"
+  my $opt_name = "$opt";
+
   # Convert - to _ in option name
-  $opt =~ s/-/_/g;
+  $opt_name =~ s/-/_/g;
   no strict 'refs';
-  ${$opt}= $value;
+  ${$opt_name}= $value;
 }
 
 use File::Basename;

mysql-test/lib/mtr_report.pm

@@ -44,12 +44,13 @@ our $timer= 1;
 sub report_option {
   my ($opt, $value)= @_;
 
+  # Evaluate $opt as string to use "Getopt::Long::Callback legacy API"
+  my $opt_name = "$opt";
+
   # Convert - to _ in option name
-  $opt =~ s/-/_/g;
+  $opt_name =~ s/-/_/g;
   no strict 'refs';
-  ${$opt}= $value;
-
-  #print $name, " setting $opt to ", (defined $value? $value : "undef") ,"\n";
+  ${$opt_name}= $value;
 }
 
 sub _name {