Consistently use $(elf-objpfx).

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/.