x86: Support VEX/EVEX WIG encoding

x86: Support VEX/EVEX WIG encoding

Add VEXWIG, defined as 3, to indicate that the VEX.W/EVEX.W bit is
ignored by such VEX/EVEX instructions, aka WIG instructions.  Set
VexW=3 on VEX/EVEX WIG instructions.  Update assembler to check
VEXWIG when setting the VEX.W bit.

gas/

	PR gas/23642
	* config/tc-i386.c (build_vex_prefix): Check VEXWIG when setting
	the VEX.W bit.
	(build_evex_prefix): Check VEXWIG when setting the EVEX.W bit.

opcodes/

	PR gas/23642
	* i386-opc.h (VEXWIG): New.
	* i386-opc.tbl: Set VexW=3 on VEX/EVEX WIG instructions.
	* i386-tbl.h: Regenerated.