[Bug lto/85451] [offloading] Improve lto-wrapper error message when not finding mkoffload

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85451

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
Created attachment 43980
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43980&action=edit
Tentative patch