x86: Add -muse-unaligned-vector-move to assembler

x86: Add -muse-unaligned-vector-move to assembler

Unaligned load/store instructions on aligned memory or register are as
fast as aligned load/store instructions on modern Intel processors.  Add
a command-line option, -muse-unaligned-vector-move, to x86 assembler to
encode encode aligned vector load/store instructions as unaligned
vector load/store instructions.

	* NEWS: Mention -muse-unaligned-vector-move.
	* config/tc-i386.c (use_unaligned_vector_move): New.
	(encode_with_unaligned_vector_move): Likewise.
	(md_assemble): Call encode_with_unaligned_vector_move for
	-muse-unaligned-vector-move.
	(OPTION_MUSE_UNALIGNED_VECTOR_MOVE): New.
	(md_longopts): Add -muse-unaligned-vector-move.
	(md_parse_option): Handle -muse-unaligned-vector-move.
	(md_show_usage): Add -muse-unaligned-vector-move.
	* doc/c-i386.texi: Document -muse-unaligned-vector-move.
	* testsuite/gas/i386/i386.exp: Run unaligned-vector-move and
	x86-64-unaligned-vector-move.
	* testsuite/gas/i386/unaligned-vector-move.d: New file.
	* testsuite/gas/i386/unaligned-vector-move.s: Likewise.
	* testsuite/gas/i386/x86-64-unaligned-vector-move.d: Likewise.