Support signbit/xorsign/copysign/abs/neg/and/xor/ior/andn for V2HF/V4HF.

gcc/ChangeLog:

	* config/i386/i386.cc (ix86_build_const_vector): Handle V2HF
	and V4HFmode.
	(ix86_build_signbit_mask): Ditto.
	* config/i386/mmx.md (mmxintvecmode): Ditto.
	(<code><mode>2): New define_expand.
	(*mmx_<code><mode>): New define_insn_and_split.
	(*mmx_nabs<mode>2): Ditto.
	(*mmx_andnot<mode>3): New define_insn.
	(<code><mode>3): Ditto.
	(copysign<mode>3): New define_expand.
	(xorsign<mode>3): Ditto.
	(signbit<mode>2): Ditto.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/part-vect-absneghf.c: New test.
	* gcc.target/i386/part-vect-copysignhf.c: New test.
	* gcc.target/i386/part-vect-xorsignhf.c: New test.