Implement support for parsing pseudo-destructor expression with a nested-name-specifi...

Implement support for parsing pseudo-destructor expression with a nested-name-specifier, e.g.,

  typedef int Int;
  int *p;
  p->Int::~Int();

This weakens the invariant that the only types in nested-name-specifiers are tag types (restricted to class types in C++98/03). However, we weaken this invariant as little as possible, accepting arbitrary types in nested-name-specifiers only when we're in a member access expression that looks like a pseudo-destructor expression.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@96743 91177308-0d34-0410-b5e6-96231b3b80d8