[Bug testsuite/80220] relative line numbers don't work when put between braces

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80220

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
Created attachment 41056
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41056&action=edit
tentative patch