Move SHMLBA to its own header.

Move SHMLBA to its own header.

One difference between bits/shm.h headers for architectures using the
Linux kernel is the definition of SHMLBA.  This was noted in
<https://sourceware.org/ml/libc-alpha/2018-09/msg00175.html> as a
reason why even a new architecture (C-SKY) might need its own
bits/shm.h; thus, splitting it out of bits/shm.h can allow less
duplication of headers for new architectures.

This patch moves that definition to its own header, bits/shmlba.h, to
allow more sharing of headers between architectures.  That move allows
the arm, ia64 and sh variants of bits/shm.h to be removed, as they had
no other significant differences from the generic bits/shm.h; powerpc
and x86 have their own bits/shm.h but do not need to get their own
bits/shmlba.h because they use the same SHMLBA as the generic header.
Other architectures with their own bits/shm.h get their own
bits/shmlba.h without being able to remove their own bits/shm.h until
the generic one has been adapted to be able to handle more
architectures (where, in addition to the differences seen for
bits/msq.h and bits/sem.h, the position of shm_segsz in struct
shmid_ds also depends on the architecture).

Tested for x86_64 and x86, and with build-many-glibcs.py.

	* sysdeps/unix/sysv/linux/Makefile (sysdep_headers): Add
	bits/shmlba.h.
	* sysdeps/unix/sysv/linux/bits/shm.h: Include <bits/shmlba.h>.
	(SHMLBA): Remove macro.
	(__getpagesize): Remove function declaration.
	* sysdeps/unix/sysv/linux/hppa/bits/shm.h: Include
	<bits/shmlba.h>.
	(SHMLBA): Remove macro.
	* sysdeps/unix/sysv/linux/mips/bits/shm.h: Include
	<bits/shmlba.h>.
	(SHMLBA): Remove macro.
	* sysdeps/unix/sysv/linux/powerpc/bits/shm.h: Include
	<bits/shmlba.h>.
	(SHMLBA): Remove macro.
	(__getpagesize): Remove function declaration.
	* sysdeps/unix/sysv/linux/sparc/bits/shm.h: Include
	<bits/shmlba.h>.
	(SHMLBA): Remove macro.
	(__getshmlba): Remove function declaration.
	* sysdeps/unix/sysv/linux/x86/bits/shm.h: Include <bits/shmlba.h>.
	(SHMLBA): Remove macro.
	(__getpagesize): Remove function declaration.
	* sysdeps/unix/sysv/linux/arm/bits/shm.h: Remove file.
	* sysdeps/unix/sysv/linux/ia64/bits/shm.h: Likewise.
	* sysdeps/unix/sysv/linux/sh/bits/shm.h: Likewise.
	* sysdeps/unix/sysv/linux/bits/shmlba.h: New file.
	* sysdeps/unix/sysv/linux/arm/bits/shmlba.h: Likewise.
	* sysdeps/unix/sysv/linux/hppa/bits/shmlba.h: Likewise.
	* sysdeps/unix/sysv/linux/ia64/bits/shmlba.h: Likewise.
	* sysdeps/unix/sysv/linux/mips/bits/shmlba.h: Likewise.
	* sysdeps/unix/sysv/linux/sh/bits/shmlba.h: Likewise.
	* sysdeps/unix/sysv/linux/sparc/bits/shmlba.h: Likewise.