miscellaneous SEC_SMALL_DATA

This patch arranges for symbols defined in .sdata and .sbss to be
reported by nm with 'g' and 's' flags, for coff targets that support
.sdata and .sbss.

The assembler changes regarding SEC_SMALL_DATA are really just
documentation.  As far as I'm aware, this won't change any assembler
output.

bfd/
	* coff-alpha.c (alpha_ecoff_le_vec): Add SEC_SMALL_DATA to
	applicable section flags.
	* coff-mips.c (mips_ecoff_le_vec, mips_ecoff_be_vec): Likewise.
	(mips_ecoff_bele_vec): Likewise.
	* coffcode.h (sec_to_styp_flags): Set SEC_SMALL_DATA for .sdata
	and .sbss sections.
	* ecoff.c (_bfd_ecoff_new_section_hook): Likewise.
	(_bfd_ecoff_styp_to_sec_flags): Likewise.
gas/
	* config/tc-m32r.c (md_begin): Set SEC_SMALL_DATA on .scommon section.
	* config/tc-mips.c (s_change_sec): Set SEC_SMALL_DATA for .sdata
	and .sbss sections.
	* config/tc-score.c: Delete !BFD_ASSEMBLER code throughout.
	(s3_s_change_sec): Set SEC_SMALL_DATA for .sbss section.
	(s3_s_score_lcomm): Likewise.
	* config/tc-score7.c: Similarly.
	* read.c (bss_alloc): Set SEC_SMALL_DATA for .sbss section.