DWARF loader:

- Multithreading is now contained in the DWARF loader using a jobs queue and a
  pool of worker threads.

BTF encoder:
    
- The parallel reproducible BTF generation done using the new DWARF loader
  multithreading model is as fast as the old non-reproducible one and thus is
  now always performed, making the "reproducible_build" flag moot.

  The memory consumption is now greatly reduced as well.

BTF loader:

- Support for multiple BTF_DECL_TAGs pointing to same tag.

  Example:
    
      $ pfunct vmlinux -F btf -f bpf_rdonly_cast
      bpf_kfunc bpf_fastcall void *bpf_rdonly_cast(const void *obj__ign, u32 btf_id__k);

Regression tests:

- Verify that pfunct prints btf_decl_tags read from BTF.

pfunct:

- Don't print functions twice when using -f.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
