[SEH] Delete the 32-bit IR lowering for __finally blocks and use x64

[SEH] Delete the 32-bit IR lowering for __finally blocks and use x64

32-bit finally funclets are intended to be called both directly from the
parent function and indirectly from the EH runtime. Because we aren't
contorting LLVM's X86 prologue to match MSVC's, calling the finally
block directly passes in a different value of EBP than the one that the
runtime provides. We need an adapter thunk to adjust EBP to the expected
value. However, WinEHPrepare already has to solve this problem when
cleanups are not pre-outlined, so we can go ahead and rely on it rather
than duplicating work.

Now we only do the llvm.x86.seh.recoverfp dance for 32-bit SEH filter
functions.

llvm-svn: 241187