reloc_upper_bound size calculations

reloc_upper_bound size calculations

Section reloc_count is an unsigned int.  Adding one for a NULL
terminator to an array of arelent pointers can wrap the count to
zero.  Avoid that by doing the addition as longs.

	* coffgen.c (coff_get_reloc_upper_bound): Don't overflow unsigned
	int expression.
	* elf.c (_bfd_elf_get_reloc_upper_bound): Likewise.
	* elf64-sparc.c (elf64_sparc_get_reloc_upper_bound): Likewise.
	* mach-o.c (bfd_mach_o_get_reloc_upper_bound): Likewise.
	* vms-alpha.c (alpha_vms_get_reloc_upper_bound): Likewise.