Make use of coff internal_reloc r_ignore

Set r_ignore on relocs already handled by a backend relocate_section,
rather than choosing a "do nothing" r_type.  This avoids bugs in all
three targets with in_reloc_p, which resulted in addresses being
emitted for dynamic relocs at all of these "do nothing" relocs.

	* coff-aarch64.c (coff_pe_aarch64_relocate_section): Leave r_type
	unchanged on relocs handled here.  Set r_ignore instead.
	* coff-i386.c (coff_pe_i386_relocate_section): Likewise.
	* coff-x86_64.c (coff_pe_amd64_relocate_section): Likewise.
	Cosmetic fix in r_type handled here.  Formatting.