Use --batch when invoking gdb, to make sure it will exit in case of an error in the command files.

mysql-test/lib/My/CoreDump.pm

@@ -35,7 +35,7 @@ sub _gdb {
     "quit\n";
 
   # Find out name of binary that generated core
-  my $list= `gdb -c $core_name -x $tmp_name -q 2>&1`
+  my $list= `gdb -c $core_name -x $tmp_name -q --batch 2>&1`
     or return;
 
   my $binary;
@@ -49,7 +49,7 @@ sub _gdb {
 
   print "Generated by '$binary'\n";
 
-  my $list= `gdb $binary -c $core_name -x $tmp_name -q 2>&1`
+  my $list= `gdb $binary -c $core_name -x $tmp_name -q --batch 2>&1`
     or return;
 
   print $list, "\n";