Initial implementation of parsing, semantic analysis, and AST-building

Initial implementation of parsing, semantic analysis, and AST-building
for constructor initializations, e.g.,

  class A { };
  class B : public A {
    int m;
  public:
    B() : A(), m(17) { };
  };

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@58749 91177308-0d34-0410-b5e6-96231b3b80d8