Add -mx86-used-note=[yes|no] option to generate (or not) GNU property
notes with GNU_PROPERTY_X86_FEATURE_2_USED and GNU_PROPERTY_X86_ISA_1_USED
properties.  If the assembly input contains no instructions, set the
GNU_PROPERTY_X86_UINT32_VALID bit in GNU_PROPERTY_X86_FEATURE_2_USED
property.  Add a --enable-x86-used-note configure time option to set the
default behavior.  Set the default if the configure option is not used
to "no".

	* NEWS: Mention -mx86-used-note=[no|yes].
	* configure.ac: Add --enable-x86-used-note.  Define
	DEFAULT_X86_USED_NOTE.
	* config.in: Regenerated.
	* configure: Likewise.
	* config/tc-i386.c (x86_isa_1_used): New.
	(x86_feature_2_used): Likewise.
	(x86_used_note): Likewise.
	(_i386_insn): Add has_regmmx, has_regxmm, has_regymm and
	has_regzmm.
	(build_modrm_byte): Set i.has_regmmx, i.has_regzmm.
	i.has_regymm and i.has_regxmm.
	(x86_cleanup): New function.
	(output_insn): Update x86_isa_1_used and x86_feature_2_used.
	(OPTION_X86_USED_NOTE): New.
	(md_longopts): Add -mx86-used-note=.
	(md_parse_option): Handle OPTION_X86_USED_NOTE.
	(md_show_usage): Display -mx86-used-note=.
	* config/tc-i386.h (x86_cleanup): New prototype.
	(md_cleanup): New.
	* doc/c-i386.texi: Document -mx86-used-note=.