Summary:
Spacetime profiling showed that this was allocating a lot more than it needs
to. Switching to a `Hashtbl` makes the memory overhead go away, and halves the
memory consumption of the whole frontend on some pathological files.
This also brings the file "clang_ast_main.ml" into the infer repo, renamed to
"ClangPointers.ml" (and given an mli). It's useful to have something like
"clang_ast_main.ml" checked into the facebook-clang-plugins repo to illustrate
how to use the OCaml AST visitor generated by atdgen, but it can be simplified
to be more pedagogical instead of being the visitor used in infer.
Reviewed By: jberdine
Differential Revision: D4884383
fbshipit-source-id: 88f324a
Jules Villard