Duplicate nodes in AST

[fwendland]

While working on #2558, I've noticed that some AST nodes have duplicates. The same nodes appear more than once based on referential integrity. These duplicates prevent the creation of unique node IDs based on the AST structure.

I've identified this kind of problem for

• C/C++ (Dupliate AST nodes in C/C++ #2653)
• Python (Dupliate AST nodes in Python #2657)
• Go (Dupliate AST nodes in Go #2658)
• LLVM (Dupliate AST nodes in LLVM #2659)

I'll create sub-issues per language to provide more details.