Merge branch 'introduce btf_tracing_ids'

Song Liu says:

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Changes v2 => v3:
1. Fix bug in task_iter.c. (Kernel test robot <lkp@intel.com>)

Changes v1 => v2:
1. Add patch 2/2. (Alexei)

1/2 fixes issue with btf_task_struct_ids w/o CONFIG_DEBUG_INFO_BTF.
2/2 replaces btf_task_struct_ids with easier to understand btf_tracing_ids.
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Signed-off-by: Alexei Starovoitov <ast@kernel.org>