changing PCH file suffix from .pch to .gch

[Roger Sayle]

Geoff Keating writes:
>  /* Part of CPP library.  (include file handling)
> -   Copyright (C) 1986, 1987, 1989, 1992, 1993, 1994, 1995, 1998,
> +   Copyright (C) 1986, 1987, 1989, 1992, 1993, 1994, 1995, 1998, 2003,
>     1999, 2000, 2001, 2002 Free Software Foundation, Inc.
>     Written by Per Bothner, 1994.

I believe the convention is to keep the list of years sorted :>

Roger
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