[CodeGen] Move EHScopeStack to CGCleanup.h from CodeGenFunction.h

No functionality change.  CGCleanup.cpp provides the implementation for
EHScopeStack, so it seems more consistent to place the class definition
in CGCleanup.h.

This should also help solve a header ordering problem that I have.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@183631 91177308-0d34-0410-b5e6-96231b3b80d8
[CodeGen] Make CGCleanup.h include what it now uses

Also move CGCleanup.h to the top of CGCleanup.cpp to verify that
CGCleanup.h really includes what it needs.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@183632 91177308-0d34-0410-b5e6-96231b3b80d8