Output destructors and constructors in a more natural order.

With this patch we output the in the order
C2
C1

D2
D1
D0

Which means that a destructor or constructor that call another is output after
the callee. This is a bit easier to read IHMO and a tiny bit more efficient
as we don't put a decl in DeferredDeclsToEmit.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@196784 91177308-0d34-0410-b5e6-96231b3b80d8