* read.c (s_comm): Check S_IS_COMMON as well as S_IS_DEFINED.

	* read.c (s_comm): Check S_IS_COMMON as well as S_IS_DEFINED.
	(s_mri_common): Check S_IS_COMMON unconditionally.
	* symbols.c (colon): Check S_IS_COMMON as well as S_IS_DEFINED.
	* config/tc-alpha.c (s_alpha_comm): Likewise.
	* config/tc-mips.c (nopic_need_relax): Likewise.
	* config/tc-ppc.c (ppc_elf_lcomm): Likewise.
	(ppc_pe_comm): Likewise.
	* config/obj-elf.c (obj_elf_common): Likewise.  Set segment of
	common symbol to bfd_com_section_ptr.
	* config/tc-sparc.c (s_common): Likewise.
	(tc_gen_reloc): Likewise.