Add clwb instruction

Add clwb instruction

gas/

	* config/tc-i386.c (cpu_arch): Add .clwb.
	* doc/c-i386.texi: Document it.

opcodes/
	* i386-dis.c (PREFIX enum): Add PREFIX_0FAE_REG_6.
	(prefix_table): Add clwb.
	* i386-gen.c (cpu_flag_init): Add CPU_CLWB_FLAGS.
	(cpu_flags): Add CpuCLWB.
	* i386-opc.h (enum): Add CpuCLWB.
	(i386_cpu_flags): Add cpuclwb.
	* i386-opc.tbl: Add clwb.
	* i386-init.h: Regenerated.
	* i386-tbl.h: Likewise.

gas/testsuite/

	* gas/i386/i386.exp: Run new tests.
	* gas/i386/clwb-intel.d: New file.
	* gas/i386/clwb.d: Likewise.
	* gas/i386/clwb.s: Likewise.
	* gas/i386/x86-64-clwb-intel.d: Likewise.
	* gas/i386/x86-64-clwb.d: Likewise.
	* gas/i386/x86-64-clwb.s: Likewise.