Fix stripping relocs in a file with mergeable notes.

Fix stripping relocs in a file with mergeable notes.

  A recent Fedora bug (1520805) exposed a problem with objcopy's reloc
  copying code, when a binary also contains mergeable notes.  The note
  merging code would delete some relocs, but then the reloc copying code
  would try to put them back again, which did not work.

  So I am checking in the patch below to fix the problem.  The patch
  also tweaks one of the binutils note merging tests so that it is
  skipped for the Sparc64 target, since this has funky relocs.

binutils	* objcopy.c (copy_relocations_in_section): Use the orelocations
	field of the input section, if it has been initialised.
	* testsuite/binutils-all/note-2-64.d: Skip test on Sparc64.

bfd	* elfcode.h (elf_write_relocs): Check for an empty howto field.