Refactor ConvertGenericCallExpr

[lucic71]

ConvertGenericCallExpr is a messy function and it became difficult to add new functoinality on top of it. So I decided to refactor it into: EmitCall(CollectCallInfo(expr)).

In the near future I plan to add 3 new features on top of it:

1. Don't hoist arguments that are integer literals, they don't alias with any other argument
2. Don't hoist if all passed arguments are local variables and all have non-reference/non-pointer types, local variables don't alias each other
3. Translate mapped (variadic) functions that have a direct mapping in libc, for example fcntl -> libc::fcntl

In the new version of ConvertGenericCallExpr, CollectCallInfo is responsible for returning the call information:

  struct CallArg {
    enum class Kind {
      Hoisted,
      Inline,
      Materialized,
    };

    clang::Expr *expr;
    Kind kind;
    std::string param_name;
    clang::QualType param_type;
    bool has_default;
    std::string ref_temp_name;
  };

  struct CallInfo {
    clang::Expr *callee;
    bool is_variadic;
    bool is_fn_ptr_call;
    std::vector<CallArg> args;
    std::vector<clang::Expr *> variadic_args;
  };

And EmitCall is responsible for emitting the hoisted arguments, the callee and the argument list using a CallInfo.

This model makes the addition of new strategies, for example Don't hoist arguments that are integer literals, they don't alias with any other argument, easier because only the CallInfo fields have to be modified.