[Bug sanitizer/81986] sanitizer detects negation of large number in string.c

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81986

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Vittorio Zecca from comment #2)
> I do not know if this is a libgfortran or a sanitizer bug.
> 
> What I do know is that changing string.c:199 from
> 
> t = - n;
> 
> into
> 
> t = -(GFC_UINTEGER_LARGEST)n;

This is of course the right fix, negation of smallest signed number is UB in C,
while it is well defined when the negation is performed in corresponding
unsigned type.