Merge branch 'bpf: Add 64bit enum value support'

Yonghong Song says:

====================

Currently, btf only supports upto 32bit enum value with BTF_KIND_ENUM.
But in kernel, some enum has 64bit values, e.g., in uapi bpf.h, we have
  enum {
        BPF_F_INDEX_MASK                = 0xffffffffULL,
        BPF_F_CURRENT_CPU               = BPF_F_INDEX_MASK,
        BPF_F_CTXLEN_MASK               = (0xfffffULL << 32),
  };
With BTF_KIND_ENUM, the value for BPF_F_CTXLEN_MASK will be encoded
as 0 which is incorrect.

To solve this problem, BTF_KIND_ENUM64 is proposed in this patch set
to support enum 64bit values. Also, since sometimes there is a need
to generate C code from btf, e.g., vmlinux.h, btf kflag support
is also added for BTF_KIND_ENUM and BTF_KIND_ENUM64 to indicate
signedness, helping proper value printout.

Changelog:
  v4 -> v5:
    - skip newly-added enum64 C test if clang version <= 14.
  v3 -> v4:
    - rename btf_type_is_any_enum() to btf_is_any_enum() to favor
      consistency in libbpf.
    - fix sign extension issue in btf_dump_get_enum_value().
    - fix BPF_CORE_FIELD_SIGNED signedness issue in bpf_core_calc_field_relo().
  v2 -> v3:
    - Implement separate btf_equal_enum()/btf_equal_enum64() and
      btf_compat_enum()/btf_compat_enum64().
    - Add a new enum64 placeholder type dynamicly for enum64 sanitization.
    - For bpftool output and unit selftest, printed out signed/unsigned
      encoding as well.
    - fix some issues with BTF_KIND_ENUM is doc and clarified sign extension
      rules for enum values.
  v1 -> v2:
    - Changed kflag default from signed to unsigned
    - Fixed sanitization issue
    - Broke down libbpf related patches for easier review
    - Added more tests
    - More code refactorization
    - Corresponding llvm patch (to support enum64) is also updated
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>