[IslExprBuilder] Print accessed memory locations with RuntimeDebugBuilder

After this change, enabling -polly-codegen-add-debug-printing in combination
with -polly-codegen-generate-expressions allows us to instrument the compiled
binaries to not only print the values stored and loaded to a given memory
access, but also to print the accessed location with array name and
per-dimension offset:

  MemRef_A[3][2]
  Store to  6299784: 5.000000
  MemRef_A[3][3]
  Load from 6299788: 0.000000
  MemRef_A[3][3]
  Store to  6299788: 6.000000

This can be very helpful for debugging.

llvm-svn: 298194