[Bug sanitizer/81604] Ubsan type reporting can be bogus in some cases

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81604

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 41858
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41858&action=edit
gcc8-pr81604.patch

Untested fix.