Setting sh_link for SHT_REL/SHT_RELA

It's wrong to have an alloc reloc section trying to use a non-alloc
symbol table.

	* elf.c (assign_section_numbers <SHT_REL, SHT_RELA>): Correct
	comment.  Always set sh_link to .dynsym for alloc reloc
	sections and to .symtab for non-alloc.