[AArch64] Allow COPY relocation elimination

[AArch64] Allow COPY relocation elimination

  As discussed at the PR, this patch tries to avoid COPY relocation generation
and propagate the original relocation into runtime if it was relocating on
writable section.  The ELIMINATE_COPY_RELOCS has been set to true and it's
underlying infrastructure has been improved so that the COPY reloc elimination
at least working on absoluate relocations (ABS64) on AArch64.

  BFD linker copy relocation elimination framwork requires the backend to always
allocate dynrelocs for all those relocation types that are possible to introduce
copy relocations.  This is for adjust_dynamic_symbol hook to be able to get all
symbol reference information.  Should one symbol is referenced by more than one
relocations, if there is any of them needs copy relocation then linker should
generate it.

bfd/
	PR ld/21532
	* elfnn-aarch64.c (ELIMINATE_COPY_RELOCS): Set to 1.
	(elfNN_aarch64_final_link_relocate): Also propagate relocations to
	runtime for if there needs copy relocation elimination.
	(need_copy_relocation_p): New function.  Return true for symbol with
	pc-relative references and if it's against read-only sections.
	(elfNN_aarch64_adjust_dynamic_symbol): Use need_copy_relocation_p.
	(elfNN_aarch64_check_relocs): Allocate dynrelocs for relocation types
	that are related with accessing external objects.
	(elfNN_aarch64_gc_sweep_hook): Sync the relocation types with the change
	in elfNN_aarch64_check_relocs.

ld/
	* testsuite/ld-aarch64/copy-reloc-exe-2.s: New test source file.
	* testsuite/ld-aarch64/copy-reloc-2.d: New test.
	* testsuite/ld-aarch64/copy-reloc-exe-eliminate.s: New test source file.
	* testsuite/ld-aarch64/copy-reloc-eliminate.d: New test.
	* testsuite/ld-aarch64/copy-reloc-so.s: Define new global objects.
	* testsuite/ld-aarch64/aarch64-elf.exp: Run new tests.