Adjust _Unwind_Word in unwind.h to version in libgcc.

Adjust _Unwind_Word in unwind.h to version in libgcc.

Building glibc on s390-32 with gcc option -mzarch produces the error due to
sysdeps/s390/jmpbuf-unwind.h:37:10: (void *) (_Unwind_GetCFA  (_context):
cast to pointer from integer of different size [-Werror=int-to-pointer-cast]

Building on s390-32 in esa-mode or s390-64 is fine.

_Unwind_GetCFA returns an _Unwind_Word which is an unsigned
with a size of 4 bytes on s390-32 (esa-mode) and 8 bytes on s390-64.
On s390-32 (zarch-mode), _Unwind_Word has a size of 8 bytes, too.

_Unwind_Word is defined in sysdeps/generic/unwind.h as
typedef unsigned _Unwind_Word __attribute__((__mode__(__word__)));

In libgcc unwind header (<gcc-src>/libgcc/unwind-generic.h) this typedef has
changed to "typedef unsigned _Unwind_Word __attribute__((__mode__(__unwind_word__)));"
in June 2008.

With this mode, _Unwind_Word has a size of 4 bytes on s390-32 (zarch-mode).
The same change applies to _Unwind_Sword.
Thus this patch updates the unwind header according to these changes.

Afterwards, the int-to-pointer-cast-warning is gone away on s390-32 (zarch-mode)
and the testsuite runs with the same test-failures as s390-32 (esa-mode)
plus FAIL: c++-types-check. Here register_t is expected to has a size of 4 bytes,
but it has a size of 8 bytes due to:
posix/sys/types.h:205:typedef int register_t __attribute__ ((__mode__ (__word__)));

The libgcc-patch for gcc 4.4 can be found here:
"[PATCH, spu, unwind] Remove attribute ((mode (word))) from unwind.h"
https://gcc.gnu.org/ml/gcc-patches/2008-06/msg00969.html

ChangeLog:

	* sysdeps/generic/unwind.h
	(_Unwind_Word): Use __mode__(__unwind_word__)
	instead of __mode__(__word__).
	(_Unwind_Sword): Likewise.