[Bug testsuite/80221] Contrib script to rewrite testcase from absolute to relative line numbers

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80221

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
Created attachment 41057
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41057&action=edit
tentative patch

This script tries to rewrite all tests, but that's not entirely supported yet.

Known error causes:
- PR80219 relative line numbers only working if gcc_{error,warning}_prefix
  defined
- PR80220 relative line numbers don't work when put between braces