Replace "link" with "sh_link"

On Linux/x86, GCC 4.2 issues a warning:

bfd/elf.c: In function ‘_bfd_elf_copy_private_bfd_data’:
bfd/elf.c:1334: warning: declaration of ‘link’ shadows a global declaration
/usr/include/unistd.h:757: warning: shadowed declaration is here
make[6]: *** [elf.lo] Error 1

Replace "link" with "sh_link" fixes it.

	* elf.c (_bfd_elf_copy_private_bfd_data): Replace "link" with
	"sh_link".