[mc] Do not try to handle scopes inside a subprogram

[mc] Do not try to handle scopes inside a subprogram

The variables of a subprogram scopes were merged in the information
about subprogram without any information on its range of validity (for
which range of IP the variable is valid).

As this handling of scopes was broken, this commit ignore the scopes within a
subprogram.

We need to:

  * either add frame_t as child of frame_t to represent scope;

  * or attach validity information on each variables

    This one is needed anyway in order to handle DW_AT_start_scope.

  * or both.

    Use frame_t for DW_TAG_inlined_subprogram and validity range for
    real scope.

-    if(dwarf_offdie(dwarf, offset+length, &die)!=NULL) {
-      MC_dwarf_handle_die(info, &die, &die, NULL);
+    if(dwarf_offdie(dwarf, offset+length, &unit_die)!=NULL) {
+      Dwarf_Die child;
+      int res;
+      for (res=dwarf_child(&unit_die, &child); res==0; res=dwarf_siblingof(&child,&child)) {
+        MC_dwarf_handle_die(info, &child, &unit_die, NULL);
+      }
     }
     offset = next_offset;
   }