WIP: Remove DW_TAG_atomic_type when encoding BTF

As BTF has no support for those types, just point tags that have as its
type an atomic to the type the atomic points to, i.e. removing the
DW_TAG_atomic_type from the type chain prior to passing it to BTF to
dedup.

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