CodeGen: Have 'this'-returning constructors and destructors to take advantage of the new backend 'returned' attribute.

The backend will now use the generic 'returned' attribute to form tail calls where possible, as well as avoid save-restores of 'this' in some cases (specifically the cases that matter for the ARM C++ ABI).

This patch also reverts a prior front-end only partial implementation of these optimizations, since it's no longer required.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184205 91177308-0d34-0410-b5e6-96231b3b80d8
Objective-C: Fixes a typo correction bug where a
selector would be correted to identical selector name
in certain corner cases. // rdar://7853549


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184208 91177308-0d34-0410-b5e6-96231b3b80d8
PR14503: Don't assert if a constexpr constructor temploid instantiates to a
constructor that does not initialize all members, and that constructor is used
to initialize a global.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184211 91177308-0d34-0410-b5e6-96231b3b80d8