Quick: Fix and enable DCE and improve GVN/DCE cleanup.

When eliminating a move by renaming its source register,
check that it doesn't conflict with vreg usage by insns
between the defining insn and the move.

Improve the GVN/DCE cleanup so that it can handle cases
where GVN or DCE is individually disabled in the pass driver
but not in the disable_opt flags.

Bug: 19419671
Change-Id: I49bb67b81509f51fbaf90c6016c509962be43736
8 files changed