Fix sign extension in cpplex.c

[Neil Booth]

Andreas Jaeger wrote:-

> The testcase I used is the following:
> 
> int
> main (void)
> {
>   signed char c = '\xff';
>   unsigned char d = '\xff';
>   
>   return 0;
> }
> 
> Ok to add this as gcc.c-torture/compile/<today>.c?  Or where should it
> get added?

Put it in gcc.dg/cpp/charconst-2.c

with a brief comment describing what the bug was.  You'll need to add
some comments like

/* { dg-do compile } */

as well, to tell dejagnu what to do.  See the many examples in that
directory.

Thanks,

Neil.