[PATCH:ico] Replace local checks for gcc with _X_NORETURN from xproto 7.0.17

[Mark Kettenis]

> From: Alan Coopersmith <alan.coopersmith at oracle.com>
> Date: Wed,  8 Jun 2011 00:04:34 -0700
> 
> Also declare icoFatal as static since it's only used in this one file.
> 
> Signed-off-by: Alan Coopersmith <alan.coopersmith at oracle.com>

Reviewed-by: Mark Kettenis <kettenis at openbsd.org>

> ---
>  configure.ac |    2 +-
>  ico.c        |    9 ++++-----
>  2 files changed, 5 insertions(+), 6 deletions(-)