[WinEH] Insert the catchpad return before CSR restoration

[WinEH] Insert the catchpad return before CSR restoration

x64 catchpads use rax to inform the unwinder where control should go
next.  However, we must initialize rax before the epilogue sequence so
as to not perturb the unwinder.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249910 91177308-0d34-0410-b5e6-96231b3b80d8