i#893 safeseh: follow-up to remove 64-bit warnings
i#893 safeseh: follow-up to remove 64-bit warnings

Removes /safeseh from ml64 as we get a warning for 64-bit where the flag is
not supported.

Review-URL: https://codereview.appspot.com/263080043

AmesianX/dynamorio,daksunt/dynamorio,daksunt/dynamorio,code4bones/dynamorio,code4bones/dynamorio,AmesianX/dynamorio,daksunt/dynamorio,AmesianX/dynamorio,code4bones/dynamorio,daksunt/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,code4bones/dynamorio,daksunt/dynamorio,code4bones/dynamorio