dwarves: Introduce type_id_t for use with the type IDs

This is just a prep patch, marking uint16_t IDs as type_id_t, that
points to uint16_t, so no change in the resulting code.

Cc: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
10 files changed