More refactoring around constructor/destructor code generation.

More refactoring around constructor/destructor code generation.
Fix some bugs with function-try-blocks and simplify normal try-block
code generation.

This implementation excludes a deleting destructor's call to
operator delete() from the function-try-block, which I believe
is correct but which I can't find straightforward support for at
a moment's glance.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@96670 91177308-0d34-0410-b5e6-96231b3b80d8