Refactor handling of conditional branches with known result.

Detect IF_cc and IF_ccZ instructions with known results in
the basic block optimization phase (instead for the codegen
phase) and replace them with GOTO/NOP. Kill blocks that are
unreachable as a result.

Change-Id: I169c2fa6f1e8af685f4f3a7fe622f5da862ce329
4 files changed