[WinEH] Split the landingpad BB instead of cloning it

This means we don't have to RAUW the landingpad instruction and
landingpad BB, which is a nice win.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235725 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed