Do not share a single unknown val# for all the live ranges merged into a...

Do not share a single unknown val# for all the live ranges merged into a physical sub-register live interval. When coalescer is merging in clobbered virtaul register live interval into a physical register live interval, give each virtual register val# a separate val# in the physical register live interval. Otherwise, the coalescer would have lost track of the definitions   information it needs to make correct coalescing decisions.

llvm-svn: 70026