Introduce ASTNode class into the AST library.

ASTNode is an immutable pair of a Decl and Stmt. If Stmt is not null, Decl should be its immediate parent.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@74797 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed