Fix PR 18369: [Thumbv8] asserts due to inconsistent CPSR liveness of IT blocks

The issue is caused when Post-RA scheduler reorders a bundle instruction
(IT block). However, it only flips the CPSR liveness of the bundle instruction,
leaves the instructions inside the bundle unchanged, which causes inconstancy and crashes
Thumb2SizeReduction.cpp::ReduceMBB().

llvm-svn: 199127