Move binpac code into the main Zeek repository

This is based on commit 48f75b5f6415fe9d597e3e991cec635b1bc400dc from
the binpac repository.

tools/binpac/src/pac_enum.h

@@ -0,0 +1,35 @@
+#ifndef pac_enum_h
+#define pac_enum_h
+
+#include "pac_decl.h"
+
+class Enum {
+public:
+    Enum(ID* id, Expr* expr = 0);
+    ~Enum();
+
+    void GenHeader(Output* out_h, int* pval);
+
+private:
+    ID* id_;
+    Expr* expr_;
+};
+
+class EnumDecl : public Decl {
+public:
+    EnumDecl(ID* id, EnumList* enumlist);
+    ~EnumDecl() override;
+
+    Type* DataType() const { return datatype_; }
+
+    void Prepare() override;
+    void GenForwardDeclaration(Output* out_h) override;
+    void GenCode(Output* out_h, Output* out_cc) override;
+
+private:
+    EnumList* enumlist_;
+    Type* datatype_;
+    TypeDecl* extern_typedecl_;
+};
+
+#endif // pac_enum_h