Various OpenACC reduction enhancements - ME and nvptx changes

Various OpenACC reduction enhancements - ME and nvptx changes

Parts of the first posting got lost in the second posting, above.
This version hopefully contains everything.

2018-10-30  Cesar Philippidis  <cesar@codesourcery.com>

	gcc/
	* config/nvptx/nvptx.c (nvptx_propagate_unified): New.
	(nvptx_split_blocks): Call it for cond_uni insn.
	(nvptx_expand_cond_uni): New.
	(enum nvptx_builtins): Add NVPTX_BUILTIN_COND_UNI.
	(nvptx_init_builtins): Initialize it.
	(nvptx_expand_builtin):
	(nvptx_generate_vector_shuffle): Change integral SHIFT operand to
	tree BITS operand.
	(nvptx_vector_reduction): New.
	(nvptx_adjust_reduction_type): New.
	(nvptx_goacc_reduction_setup): Use it to adjust the type of ref_to_res.
	(nvptx_goacc_reduction_init): Don't update LHS if it doesn't exist.
	(nvptx_goacc_reduction_fini): Call nvptx_vector_reduction for vector.
	Use it to adjust the type of ref_to_res.
	(nvptx_goacc_reduction_teardown):
	* config/nvptx/nvptx.md (cond_uni): New pattern.

(cherry picked from openacc-gcc-9-branch commit
6f456aa7d21e587debff82f3cbf89750528018d1)