Split the landing pad's edge. Then for all uses of a landingpad instruction's

Split the landing pad's edge. Then for all uses of a landingpad instruction's
value, we insert a load of the exception object and selector object from memory,
which is where it actually resides. If it's used by a PHI node, we follow that
to where it is being used. Eventually, all landingpad instructions should have
no uses. Any PHI nodes that were associated with those landingpads should be
removed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@138302 91177308-0d34-0410-b5e6-96231b3b80d8