bpf: implementation of func_info in .BTF.ext.

bpf: implementation of func_info in .BTF.ext.

Kernel verifier complains in some particular cases for missing func_info
implementation in .BTF.ext. This patch implements it.

Strings are cached locally in coreout.cc to avoid adding duplicated
strings in the string list. This string deduplication should eventually
be moved to the CTFC functions such that this happens widely.

With this implementation, the CO-RE relocations information was also
simplified and integrated with the FuncInfo structures.

gcc/Changelog:

	PR target/113453
	* config/bpf/bpf.cc (bpf_function_prologue): Define target
	hook.
	* config/bpf/coreout.cc (brf_ext_info_section)
	(btf_ext_info): Move from coreout.h
	(btf_ext_funcinfo, btf_ext_lineinfo): Add struct.
	(bpf_core_reloc): Rename to btf_ext_core_reloc.
	(btf_ext): Add static variable.
	(btfext_info_sec_find_or_add, SEARCH_NODE_AND_RETURN)
	(bpf_create_or_find_funcinfo, bpt_create_core_reloc)
	(btf_ext_add_string, btf_funcinfo_type_callback)
	(btf_add_func_info_for, btf_validate_funcinfo)
	(btf_ext_info_len, output_btfext_func_info): Add function.
	(output_btfext_header, bpf_core_reloc_add)
	(output_btfext_core_relocs, btf_ext_init, btf_ext_output):
	Change to support new structs.
	* config/bpf/coreout.h (btf_ext_funcinfo, btf_ext_lineinfo):
	Move and change in coreout.cc.
	(btf_add_func_info_for, btf_ext_add_string): Add prototypes.

gcc/testsuite/ChangeLog:
	PR target/113453
	* gcc.target/bpf/btfext-funcinfo-nocore.c: Add.
	* gcc.target/bpf/btfext-funcinfo.c: Add.
	* gcc.target/bpf/core-attr-5.c: Fix regexp.
	* gcc.target/bpf/core-attr-6.c: Fix regexp.
	* gcc.target/bpf/core-builtin-fieldinfo-offset-1.c: Fix regexp.
	* gcc.target/bpf/core-section-1.c: Fix regexp.