Remove miscellaneous debris from libio.

Remove miscellaneous debris from libio.

This patch eliminates a number of #if 0 and #ifdef TODO blocks, macros
that are never used, macros that provide portability to substrates that
lack basic things like EINVAL and off_t, and other such debris.

I preserved IO_DEBUG and CHECK_FILE, even though as far as I can tell
IO_DEBUG is never defined and therefore CHECK_FILE never does
anything, because it seems like we might actually want to turn it _on_.

Installed stripped libraries and executables are unchanged, except,
again, that the line number of an assertion changes (this time it's
somewhere in fileops.c).

	* libio/libio.h (_IO_pos_BAD, _IO_pos_0, _IO_pos_adjust):
	Define here, unconditionally.
	* libio/iolibio.h (_IO_pos_BAD): Don't define here.
	* libio/libioP.h: Remove #if 0 blocks.
	(_IO_pos_BAD, _IO_pos_0, _IO_pos_adjust): Don't define here.
	(_IO_va_start, COERCE_FILE, MAYBE_SET_EINVAL): Don't define.
	(CHECK_FILE): Don't use MAYBE_SET_EINVAL or COERCE_FILE.  Fix style.

	* libio/clearerr.c, libio/fputc.c, libio/getchar.c:
	Assume weak_alias is always defined.

	* libio/fileops.c, libio/genops.c, libio/oldfileops.c
	* libio/oldpclose.c, libio/pclose.c, libio/wfileops.c:
	Remove #if 0 and #ifdef TODO blocks.
	Assume text_set_element is always defined.

	* libio/iofdopen.c, libio/iogetdelim.c, libio/oldiofdopen.c
	Use __set_errno (EINVAL) instead of MAYBE_SET_EINVAL.
	* libio/tst-mmap-eofsync.c: Make #if 1 block unconditional.