Extraneous newline emitted between error messages in GCC 6

[Marek Polacek]

On Mon, Dec 21, 2015 at 01:12:33PM -0500, Patrick Palka wrote:
> GCC 6, compared to GCC 5, now emits an extra newline between error
> messages.  Is this intended?
> 
> $ cat error.c
> int x = a;
> int y = b;
> $ gcc-5 error.c
> error.c:1:9: error: ‘a’ undeclared here (not in a function)
>  int x = a;
>          ^
> error.c:2:9: error: ‘b’ undeclared here (not in a function)
>  int y = b;
>          ^
> $ gcc-6 error.c
> error.c:1:9: error: ‘a’ undeclared here (not in a function)
>  int x = a;
>          ^
> 
> error.c:2:9: error: ‘b’ undeclared here (not in a function)
>  int y = b;
>          ^
> 
> $

Started with r229884: Reimplement diagnostic_show_locus, introducing
rich_location classes.  I think it is a bug and should be fixed.

	Marek