[goalc] Cleaned up speedups (#3066)

Started at 349,880,038 allocations and 42s

- Switched to making `Symbol` in GOOS be a "fixed type", just a wrapper
around a `const char*` pointing to the string in the symbol table. This
is a step toward making a lot of things better, but by itself not a huge
improvement. Some things may be worse due to more temp `std::string`
allocations, but one day all these can be removed. On linux it saved
allocations (347,685,429), and saved a second or two (41 s).
- cache `#t` and `#f` in interpreter, better lookup for special
forms/builtins (hashtable of pointers instead of strings, vector for the
small special form list). Dropped time to 38s.
- special-case in quasiquote when splicing is the last thing in a list.
Allocation dropped to 340,603,082
- custom hash table for environment lookups (lexical vars). Dropped to
36s and 314,637,194
- less allocation in `read_list` 311,613,616. Time about the same.
- `let` and `let*` in Interpreter.cpp 191,988,083, time down to 28s.

goalc/make/MakeSystem.cpp

@@ -136,7 +136,7 @@ goos::Object MakeSystem::handle_defstep(const goos::Object& form,
     step->outputs.push_back(m_path_map.apply_remaps(obj.as_string()->data));
   });
 
-  step->tool = args.get_named("tool").as_symbol()->name;
+  step->tool = args.get_named("tool").as_symbol().name_ptr;
 
   if (m_tools.find(step->tool) == m_tools.end()) {
     throw std::runtime_error(fmt::format("The tool {} is unknown.", step->tool));
@@ -232,7 +232,7 @@ goos::Object MakeSystem::handle_get_gsrc_path(const goos::Object& form,
   if (m_gsrc_files.count(file_name) != 0) {
     return goos::StringObject::make_new(m_gsrc_files.at(file_name));
   } else {
-    return goos::SymbolObject::make_new(m_goos.reader.symbolTable, "#f");
+    return goos::Object::make_symbol(&m_goos.reader.symbolTable, "#f");
   }
 }