[debug-early] LTO streaming of on-the-side dwarf data structures

[Aldy Hernandez]

> Another similar issue I've seen is handling DW_TAG_lexical_block
> (gen_lexical_block_die).  Ideally we should generate the
> DW_TAG_lexical_block and the corresponding locals in early dumping, and
> then fill in the high/low attributes of the lexical block the second
> time around.  We would need a hash similar to decl_die_table to get from
> BLOCK->DW_TAG_lexical_block, similar to die_table_offset.  For that
> matter, we could store the relationship in die_table_offset, or in the
> die_offset if I understood things correctly.

Errr, we can't store a TREE->DW_TAG_lexical_block relationship in 
die_table_offset cause we don't have a DECL_UID.  So we need another 
mechanism.

Aldy