[OpenCL] Improve destructor support in C++ for OpenCL

Summary:
This patch does mainly three things:
 1. It fixes a false positive error detection in Sema that is similar to
    D62156. The error happens when explicitly calling an overloaded
    destructor for different address spaces.
 2. It selects the correct destructor when multiple overloads for
    address spaces are available.
 3. It inserts the expected address space cast when invoking a
    destructor, if needed, and therefore fixes a crash due to the unmet
    assertion in llvm::CastInst::Create.

The following is a reproducer of the three issues:

    struct MyType {
      ~MyType() {}
      ~MyType() __constant {}
    };

    __constant MyType myGlobal{};

    kernel void foo() {
      myGlobal.~MyType(); // 1 and 2.
      // 1. error: cannot initialize object parameter of type
      //    '__generic MyType' with an expression of type '__constant MyType'
      // 2. error: no matching member function for call to '~MyType'
    }

    kernel void bar() {
      // 3. The implicit call to the destructor crashes due to:
      //    Assertion `castIsValid(op, S, Ty) && "Invalid cast!"' failed.
      //    in llvm::CastInst::Create.
      MyType myLocal;
    }

The added test depends on D62413 and covers a few more things than the
above reproducer.

Subscribers: yaxunl, Anastasia, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D64569

llvm-svn: 366422