[llvm-pdbutil] Show what blocks a stream occupies.

[llvm-pdbutil] Show what blocks a stream occupies.

This is useful when you want to look at a specific chunk of a
stream or look for discontinuities, and you need to know the
list of blocks occupied by a stream.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306150 91177308-0d34-0410-b5e6-96231b3b80d8