Don't generate empty reloc sections

Don't generate empty reloc sections

binutils/

	PR binutils/13947
	* objcopy.c (copy_object): Call copy_relocations_in_section
	before copy_section.
	(skip_section): New.
	(copy_relocations_in_section): Likewise.
	(copy_section): Use skip_section.  Don't copy relocations here.

binutils/testsuite/

	PR binutils/13947
	* binutils-all/i386/compressed-1b.d: Remove empty REL section.
	* binutils-all/i386/compressed-1c.d: Likewise.

	* binutils-all/x86-64/compressed-1b.d: Remove empty RELA
	section.
	* binutils-all/x86-64/compressed-1c.d: Likewise.