Remove obsolete ARC system

Remove obsolete ARC system

ARC architecture specific files has been added ages ago in newlib/libc/sys,
but with invention of libgloss those files should be moved from newlib to
libgloss.

newlib/ChangeLog:
2015-11-12  Anton Kolesov  <Anton.Kolesov@synopsys.com>

	* configure.host: Remove ARC system.
	* libc/sys/configure: Likewise.
	* libc/sys/configure.in: Likewise.
	* libc/sys/arc/Makefile.am: Likewise.
	* libc/sys/arc/Makefile.in: Likewise.
	* libc/sys/arc/aclocal.m4: Likewise.
	* libc/sys/arc/configure: Likewise.
	* libc/sys/arc/configure.in: Likewise.
	* libc/sys/arc/crt0.S: Likewise.
	* libc/sys/arc/dummy.S: Likewise.
	* libc/sys/arc/isatty.c: Likewise.
	* libc/sys/arc/mem-layout.c: Likewise.
	* libc/sys/arc/sbrk.c: Likewise.
	* libc/sys/arc/sys/syscall.h: Likewise.
	* libc/sys/arc/syscalls.c: Likewise.