rs6000: Consolidate target built-ins code

Continuing with the refactoring effort, this patch moves as much of the
target-specific built-in support code into a new file, rs6000-builtin.cc.
However, we can't easily move the overloading support code out of
rs6000-c.cc, because the build machinery understands that as a special file
to be included with the C and C++ front ends.

This patch is just a straightforward move, with one exception.  I found
that the builtin_mode_to_type[] array is no longer used, so I also removed
all code having to do with it.

The code in rs6000-builtin.cc is organized in related sections:
 - General support functions
 - Initialization support
 - GIMPLE folding support
 - Expansion support

Overloading support remains in rs6000-c.cc.

2022-02-03  Bill Schmidt  <wschmidt@linux.ibm.com>

gcc/
	* config.gcc (powerpc*-*-*): Add rs6000-builtin.o to extra_objs.
	* config/rs6000/rs6000-builtin.cc: New file, containing code moved
	from other files.
	* config/rs6000/rs6000-call.cc (cpu_is_info): Move to
	rs6000-builtin.cc.
	(cpu_supports_info): Likewise.
	(rs6000_type_string): Likewise.
	(altivec_expand_predicate_builtin): Likewise.
	(rs6000_htm_spr_icode): Likewise.
	(altivec_expand_vec_init_builtin): Likewise.
	(get_element_number): Likewise.
	(altivec_expand_vec_set_builtin): Likewise.
	(altivec_expand_vec_ext_builtin): Likewise.
	(rs6000_invalid_builtin): Likewise.
	(rs6000_fold_builtin): Likewise.
	(fold_build_vec_cmp): Likewise.
	(fold_compare_helper): Likewise.
	(map_to_integral_tree_type): Likewise.
	(fold_mergehl_helper): Likewise.
	(fold_mergeeo_helper): Likewise.
	(rs6000_builtin_valid_without_lhs): Likewise.
	(rs6000_builtin_is_supported): Likewise.
	(rs6000_gimple_fold_mma_builtin): Likewise.
	(rs6000_gimple_fold_builtin): Likewise.
	(rs6000_expand_ldst_mask): Likewise.
	(cpu_expand_builtin): Likewise.
	(elemrev_icode): Likewise.
	(ldv_expand_builtin): Likewise.
	(lxvrse_expand_builtin): Likewise.
	(lxvrze_expand_builtin): Likewise.
	(stv_expand_builtin): Likewise.
	(mma_expand_builtin): Likewise.
	(htm_spr_num): Likewise.
	(htm_expand_builtin): Likewise.
	(rs6000_expand_builtin): Likewise.
	(rs6000_vector_type): Likewise.
	(rs6000_init_builtins): Likewise.  Remove initialization of
	builtin_mode_to_type entries.
	(rs6000_builtin_decl): Move to rs6000-builtin.cc.
	* config/rs6000/rs6000.cc (rs6000_builtin_mask_for_load): New
	external declaration.
	(rs6000_builtin_md_vectorized_function): Likewise.
	(rs6000_builtin_reciprocal): Likewise.
	(altivec_builtin_mask_for_load): Move to rs6000-builtin.cc.
	(rs6000_builtin_types): Likewise.
	(builtin_mode_to_type): Remove.
	(rs6000_builtin_mask_for_load): Move to rs6000-builtin.cc.  Remove
	static qualifier.
	(rs6000_builtin_md_vectorized_function): Likewise.
	(rs6000_builtin_reciprocal): Likewise.
	* config/rs6000/rs6000.h (builtin_mode_to_type): Remove.
	* config/rs6000/t-rs6000 (rs6000-builtin.o): New target.