Make alpha termios.h define IXANY unconditionally (bug 21259).

sysdeps/unix/sysv/linux/alpha/bits/termios.h defines IXANY only if
__USE_MISC.  But it's in the base standard for POSIX.1:2008, and
XSI-shaded in previous standards.  This patch makes the header define
it unconditionally, like other versions of this header do (it's always
reserved by standards that don't require it, so defining
unconditionally is OK by the standards).

Tested (compilation only) for alpha with build-many-glibcs.py.  Note
that there are still termios.h conformtest failures after this patch
because of other issues with the alpha version of this header.

	[BZ #21259]
	* sysdeps/unix/sysv/linux/alpha/bits/termios.h (IXANY): Define
	unconditionally, not just for [__USE_MISC].