Except in asm-verbose mode, avoid printing labels for blocks that are

Except in asm-verbose mode, avoid printing labels for blocks that are
only reachable via fall-through edges. This dramatically reduces the
number of labels printed, and thus also the number of labels the
assembler must parse and remember.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@68073 91177308-0d34-0410-b5e6-96231b3b80d8