[WinEH] Make funclet return instrs pseudo instrs

[WinEH] Make funclet return instrs pseudo instrs

This makes catchret look more like a branch, and less like a weird use
of BlockAddress. It also lets us get away from
llvm.x86.seh.restoreframe, which relies on the old parentfpoffset label
arithmetic.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@247936 91177308-0d34-0410-b5e6-96231b3b80d8