Since tile support has been removed from the Linux kernel for 4.17,
this patch removes the (unmaintained) port to tilegx from glibc (the
tilepro support having been previously removed).  This reflects the
general principle that a glibc port needs upstream support for the
architecture in all the components it build-depends on (so binutils,
GCC and the Linux kernel, for the normal case of a port supporting the
Linux kernel but no other OS), in order to be maintainable.

Apart from removal of sysdeps/tile and sysdeps/unix/sysv/linux/tile,
there are updates to various comments referencing tile for which
removal of those references seemed appropriate.  The configuration is
removed from README and from build-many-glibcs.py.  contrib.texi keeps
mention of removed contributions, but I updated Chris Metcalf's entry
to reflect that he also contributed the non-removed support for the
generic Linux kernel syscall interface.
__ASSUME_FADVISE64_64_NO_ALIGN support is removed, as it was only used
by tile.

	* sysdeps/tile: Remove.
	* sysdeps/unix/sysv/linux/tile: Likewise.
	* README (tilegx-*-linux-gnu): Remove from list of supported
	configurations.
	* manual/contrib.texi (Contributors): Mention Chris Metcalf's
	contribution of support for generic Linux kernel syscall
	interface.
	* scripts/build-many-glibcs.py (Context.add_all_configs): Remove
	tilegx configurations.
	(Config.install_linux_headers): Do not handle tile.
	* sysdeps/unix/sysv/linux/aarch64/ldsodefs.h: Do not mention Tile
	in comment.
	* sysdeps/unix/sysv/linux/nios2/Makefile: Likewise.
	* sysdeps/unix/sysv/linux/posix_fadvise.c: Likewise.
	[__ASSUME_FADVISE64_64_NO_ALIGN] (__ALIGNMENT_ARG): Remove
	conditional undefine and redefine.
	* sysdeps/unix/sysv/linux/posix_fadvise64.c: Do not mention Tile
	in comment.
	[__ASSUME_FADVISE64_64_NO_ALIGN] (__ALIGNMENT_ARG): Remove
	conditional undefine and redefine.