[lanai] Use peephole optimizer to generate more conditional ALU operations.

Summary:
* Similiar to the ARM backend yse the peephole optimizer to generate more conditional ALU operations;
* Add predicated type with default always true to RR instructions in LanaiInstrInfo.td;
* Move LanaiSetflagAluCombiner into optimizeCompare;
* The ASM parser can currently only handle explicitly specified CC, so specify ".t" (true) where needed in the ASM test;
* Remove unused MachineOperand flags;

Reviewers: eliben

Subscribers: aemerson

Differential Revision: http://reviews.llvm.org/D22072

llvm-svn: 274807