Get rid of SEC_ELF_COMPRESS

Get rid of SEC_ELF_COMPRESS

This flag also isn't needed, except for some sanity checks which we
can omit.

	* elf.c (elf_fake_sections): Don't set SEC_ELF_COMPRESS for
	compressed debug sections, just leave sh_name as -1.
	(assign_file_positions_for_non_load_sections),
	(assign_file_positions_except_relocs): Decide whether a section
	needs compressing and thus should not have its file offset set
	by looking at sh_name.
	(_bfd_elf_assign_file_positions_for_non_load): Similarly decide
	which sections need compressing.
	* elflink.c (bfd_elf_final_link): Don't test SEC_ELF_COMPRESS.
	* merge.c (_bfd_write_merged_section): Likewise.
	* section.c (SEC_ELF_COMPRESS): Don't define.
	(SEC_ELF_PURECODE): Renumber.
	* bfd-in2.h: Regenerate.