Treat mid-block labels the same as terminators when building the

Treat mid-block labels the same as terminators when building the
MachineInstr scheduling DAG, meaning they implicitly depend on all
preceding defs. This fixes Benchmarks/Shootout-C++/except and
Regression/C++/EH/simple_rethrow in
  -relocation-model=pic -disable-post-RA-scheduler=false
mode.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@59747 91177308-0d34-0410-b5e6-96231b3b80d8