bpf: Implementation of BPF CO-RE builtins

This patch updates the support for the BPF CO-RE builtins
__builtin_preserve_access_index and __builtin_preserve_field_info,
and adds support for the CO-RE builtins __builtin_btf_type_id,
__builtin_preserve_type_info and __builtin_preserve_enum_value.

These CO-RE relocations are now converted to __builtin_core_reloc which
abstracts all of the original builtins in a polymorphic relocation
specific builtin.

The builtin processing is now split in 2 stages, the first (pack) is
executed right after the front-end and the second (process) right before
the asm output.

In expand pass the __builtin_core_reloc is converted to a
unspec:UNSPEC_CORE_RELOC rtx entry.

The data required to process the builtin is now collected in the packing
stage (after front-end), not allowing the compiler to optimize any of
the relevant information required to compose the relocation when
necessary.
At expansion, that information is recovered and CTF/BTF is queried to
construct the information that will be used in the relocation.
At this point the relocation is added to specific section and the
builtin is expanded to the expected default value for the builtin.

In order to process __builtin_preserve_enum_value, it was necessary to
hook the front-end to collect the original enum value reference.
This is needed since the parser folds all the enum values to its
integer_cst representation.

More details can be found within the core-builtins.cc.

Regtested in host x86_64-linux-gnu and target bpf-unknown-none.

gcc/ChangeLog:

	PR target/107844
	PR target/107479
	PR target/107480
	PR target/107481
	* config.gcc: Added core-builtins.cc and .o files.
	* config/bpf/bpf-passes.def: Removed file.
	* config/bpf/bpf-protos.h (bpf_add_core_reloc,
	bpf_replace_core_move_operands): New prototypes.
	* config/bpf/bpf.cc (enum bpf_builtins, is_attr_preserve_access,
	maybe_make_core_relo, bpf_core_field_info, bpf_core_compute,
	bpf_core_get_index, bpf_core_new_decl, bpf_core_walk,
	bpf_is_valid_preserve_field_info_arg, is_attr_preserve_access,
	handle_attr_preserve, pass_data_bpf_core_attr, pass_bpf_core_attr):
	Removed.
	(def_builtin, bpf_expand_builtin, bpf_resolve_overloaded_builtin): Changed.
	* config/bpf/bpf.md (define_expand mov<MM:mode>): Changed.
	(mov_reloc_core<mode>): Added.
	* config/bpf/core-builtins.cc (struct cr_builtin, enum
	cr_decision struct cr_local, struct cr_final, struct
	core_builtin_helpers, enum bpf_plugin_states): Added types.
	(builtins_data, core_builtin_helpers, core_builtin_type_defs):
	Added variables.
	(allocate_builtin_data, get_builtin-data, search_builtin_data,
	remove_parser_plugin, compare_same_kind, compare_same_ptr_expr,
	compare_same_ptr_type, is_attr_preserve_access, core_field_info,
	bpf_core_get_index, compute_field_expr,
	pack_field_expr_for_access_index, pack_field_expr_for_preserve_field,
	process_field_expr, pack_enum_value, process_enum_value, pack_type,
	process_type, bpf_require_core_support, make_core_relo, read_kind,
	kind_access_index, kind_preserve_field_info, kind_enum_value,
	kind_type_id, kind_preserve_type_info, get_core_builtin_fndecl_for_type,
	bpf_handle_plugin_finish_type, bpf_init_core_builtins,
	construct_builtin_core_reloc, bpf_resolve_overloaded_core_builtin,
	bpf_expand_core_builtin, bpf_add_core_reloc,
	bpf_replace_core_move_operands): Added functions.
	* config/bpf/core-builtins.h (enum bpf_builtins): Added.
	(bpf_init_core_builtins, bpf_expand_core_builtin,
	bpf_resolve_overloaded_core_builtin): Added functions.
	* config/bpf/coreout.cc (struct bpf_core_extra): Added.
	(bpf_core_reloc_add, output_asm_btfext_core_reloc): Changed.
	* config/bpf/coreout.h (bpf_core_reloc_add) Changed prototype.
	* config/bpf/t-bpf: Added core-builtins.o.
	* doc/extend.texi: Added documentation for new BPF builtins.

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