https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52952
--- Comment #48 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
somethin like that fixes it for me:
Index: pr66415-1.c
===================================================================
--- pr66415-1.c (revision 239624)
+++ pr66415-1.c (working copy)
@@ -1,6 +1,7 @@
/* PR c/66415 */
/* { dg-do compile } */
/* { dg-options "-Wformat -fdiagnostics-show-caret" } */
+/* { dg-set-compiler-env-var COLUMNS "82" } */
void
fn1 (void)
