Reapply commit 112702 which was speculatively reverted by echristo.

Reapply commit 112702 which was speculatively reverted by echristo.
Original commit message:
Use the SSAUpdator to turn calls to eh.exception that are not in a
landing pad into uses of registers rather than loads from a stack
slot.  Doesn't touch the 'orrible hack code - Bill needs to persuade
me harder :)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112952 91177308-0d34-0410-b5e6-96231b3b80d8