[arm][2/X] Implement __qadd, __qsub, __qdbl intrinsics

[arm][2/X] Implement __qadd, __qsub, __qdbl intrinsics

This patch implements some more Q-bit-setting intrinsics from ACLE.
With the plumbing from patch 1 in place they are a simple builtin->RTL
affair.

	* config/arm/arm.md (arm_<ss_op>): New define_expand.
	(arm_<ss_op><add_clobber_q_name>_insn): New define_insn.
	* config/arm/arm_acle.h (__qadd, __qsub, __qdbl): Define.
	* config/arm/arm_acle_builtins.def: Add builtins for qadd, qsub.
	* config/arm/iterators.md (SSPLUSMINUS): New code iterator.
	(ss_op): New code_attr.

	* gcc.target/arm/acle/dsp_arith.c: New test.

From-SVN: r277915