[AArch64] Only override the symbol dynamic decision on undefined weak symbol

[AArch64] Only override the symbol dynamic decision on undefined weak symbol

This fix is an adaption of the x86-64 PR ld/21402 fix to AArch64.

After the generic code deciding one symbol is not dynamic, AArch64 backend
only overrides the decision on undefined weak symbols.

bfd/
	PR ld/21402
	* elfnn-aarch64.c (elfNN_aarch64_allocate_dynrelocs): Only make
	undefined weak symbols into dynamic.
	(elfNN_aarch64_final_link_relocate): Generate runtime RELATIVE
	relocation for non-dynamic symbols.
	(elfNN_aarch64_finish_dynamic_symbol): Add sanity check.