[og9] AMD GCN adjustments for middle-end worker partitioning

[og9] AMD GCN adjustments for middle-end worker partitioning

	gcc/
	* config/gcn/gcn-protos.h (gcn_goacc_adjust_propagation_record): Rename
	prototype to...
	(gcn_goacc_create_propagation_record): This.
	* config/gcn/gcn-tree.c (gcn_goacc_adjust_propagation_record): Rename
	function to...
	(gcn_goacc_create_propagation_record): This.  Adjust comment.
	* config/gcn/gcn.c (gcn_init_builtins): Override decls for
        BUILT_IN_GOACC_SINGLE_START, BUILT_IN_GOACC_SINGLE_COPY_START,
        BUILT_IN_GOACC_SINGLE_COPY_END and BUILT_IN_GOACC_BARRIER.
	(gcn_fork_join): Remove inaccurate comment.
	(TARGET_GOACC_ADJUST_PROPAGATION_RECORD): Rename to...
	(TARGET_GOACC_CREATE_PROPAGATION_RECORD): This.

(cherry picked from openacc-gcc-9-branch commit
f079b7a61a6bc88109ad68fffca607b47ec109c5)