[Bug middle-end/77721] -Wformat-length not uses arg range for converted vars

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77721

--- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> ---
As it turns out, the patch for bug 78622 only masked the true root cause of the
problem which is bug 78969.  An unrelated patch I'm testing makes the false
positives come back.  There may be a way to work around the underlying problem
but I'm mot sure I'll have the time to do it in GCC 7.