Use common bits/shm.h for more architectures.

Use common bits/shm.h for more architectures.

sysdeps/unix/sysv/linux/bits/shm.h has padding after time fields in
struct shmid_ds unconditionally, and thus is only suitable for 32-bit
architectures (no 64-bit configurations use this file);
sysdeps/unix/sysv/linux/generic/bits/shm.h is substantively the same,
except that the padding is conditioned on __WORDSIZE == 32, and so it
can be used for 64-bit architectures as well.

This patch adds the conditionals to
sysdeps/unix/sysv/linux/bits/shm.h.  The linux/generic/ version is
then no longer needed and so is removed, as are the alpha and s390
versions which are also no longer needed.  The other
architecture-specific versions have different padding, layout, types
or SHMLBA definitions and so are still needed after this change.

This is essentially the same change for bits/shm.h as the bits/msq.h
patch and the bits/sem.h patch.  However, the details of the padding
variations for the architectures that aren't changed are not all the
same between msqid_ds, shmid_ds and semid_ds.

Tested with build-many-glibcs.py.

	* sysdeps/unix/sysv/linux/bits/shm.h: Include <bits/wordsize.h>.
	(struct shmid_ds): Condition padding after time fields on
	[__WORDSIZE == 32].
	* sysdeps/unix/sysv/linux/alpha/bits/shm.h: Remove file.
	* sysdeps/unix/sysv/linux/generic/bits/shm.h: Likewise.
	* sysdeps/unix/sysv/linux/s390/bits/shm.h: Likewise.