re PR debug/47106 (-fcompare-debug failure (length) with  -fpartial-inlining -flto -fconserve-stack)

PR debug/47106
PR debug/47402
* tree-flow-inline.h (clear_is_used, is_used_p): New.
* cfgexpand.c (account_used_vars_for_block): Use them.
* tree-nrv.c (tree_nrv): Likewise.
* tree-ssa-live.c (remove_unused_scope_block_p): Likewise.
(dump_scope_block): Likewise.
(remove_unused_locals): Likewise.

From-SVN: r169515