[mc] Process nested scopes DWARF informations

Subprograms contains scopes (with variables) and scope contains other
scopes as well. They are represented by the same data structure
dw_frame_t. Scopes might be :

  * DW_TAG_lexical_scope;
  * DW_try_block;
  * DW_catch_block;
  * DW_with_stmt (partial support);
  * DW_inlined_subroutine.

The scopes informations are stored but they are not used yet.