aarch64: Merge rtld_errno offset with memory reference
aarch64: Merge __local_multiple_threads offset with memory reference

This also highlights that we'd been loading 64-bits instead of
the proper 32-bits.  Caught by the linker as a relocation error,
since the variable happened to be unaligned for 64-bits.
Consistently use $(elf-objpfx).

As previously noted
<https://sourceware.org/ml/libc-alpha/2013-05/msg00696.html>,
$(elf-objpfx) and $(elfobjdir) are redundant and should be
consolidated.  This patch consolidates on $(elf-objpfx) (for
consistency with $(csu-objpfx)), also changing direct uses of
$(common-objpfx)elf/ to use $(elf-objpfx).

Tested x86_64, including that installed shared libraries are unchanged
by the patch.

	* Makeconfig [$(build-hardcoded-path-in-tests) = yes]
	(rtld-tests-LDFLAGS): Use $(elf-objpfx) instead of
	$(common-objpfx)elf/.
	(link-libc-before-gnulib): Likewise.
	(elfobjdir): Remove variable.
	* Makefile (install): Use $(elf-objpfx) instead of
	$(common-objpfx)elf/.
	* Makerules (link-libc-args): Use $(elf-objpfx) instead of
	$(elfobjdir)/.
	(link-libc-deps): Likewise.
	($(common-objpfx)libc.so): Likewise.
	($(common-objpfx)linkobj/libc.so): Likewise.
	[$(cross-compiling) = no] (symbolic-link-prog): Use $(elf-objpfx)
	instead of $(common-objpfx)elf/.
	(symbolic-link-list): Likewise.
	* iconvdata/Makefile ($(inst_gconvdir)/gconv-modules)
	[$(cross-compiling) = no]: Likewise.
	* sysdeps/arm/Makefile (gnulib-arch): Use $(elf-objpfx) instead of
	$(elfobjdir)/.
	(static-gnulib-arch): Likewise.
	* sysdeps/s390/s390-64/Makefile ($(inst_gconvdir)/gconv-modules)
	[$(cross-compiling) = no]: Use $(elf-objpfx) instead of
	$(common-objpfx)elf/.

localedata/ChangeLog:
	* Makefile (LOCALEDEF): Use $(elf-objpfx) instead of
	$(common-objpfx)elf/.
Don't mention linuxthreads in Depend files.

I noticed that some of the Depend files, used to determine the
subdirectory build order in sysd-sorted, still mentioned linuxthreads,
although it hasn't been supported for many years.  This patch removes
those references.  In the case of nscd, it substitutes an nptl
reference, since I believe there is a fact a thread library dependence
there; the others already mentioned nptl.

Note that I am not at all confident in the completeness of these
Depend files.

Note also that references to linuxthreads remain in a comment in
sysdeps/unix/sysv/linux/ia64/Versions, and in manual/maint.texi,
manual/signal.texi and scripts/documented.sh.

Tested x86_64 that the installed shared libraries are unchanged by the
patch (as is sysd-sorted).

	* nscd/Depend (linuxthreads): Remove.
	(nptl): Add.
	* resolv/Depend (linuxthreads): Remove.
	* rt/Depend (linuxthreads): Remove.
AArch64: Convert fork.c to arch-fork.h