Allow gimple_build with internal functions

Allow gimple_build with internal functions

This patch makes the function versions of gimple_build and
gimple_simplify take combined_fns rather than built_in_codes,
so that they work with internal functions too.  The old
gimple_builds were unused, so no existing callers need
to be updated.

2018-05-17  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* gimple-fold.h (gimple_build): Make the function forms take
	combined_fn rather than built_in_function.
	(gimple_simplify): Likewise.
	* gimple-match-head.c (gimple_simplify): Likewise.
	* gimple-fold.c (gimple_build): Likewise.
	* tree-vect-loop.c (get_initial_def_for_reduction): Use gimple_build
	rather than gimple_build_call_internal.
	(get_initial_defs_for_reduction): Likewise.
	(vect_create_epilog_for_reduction): Likewise.
	(vectorizable_live_operation): Likewise.

From-SVN: r260315