[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/compiler/compilation/ControlFlow.cpp

@@ -54,7 +54,7 @@ Condition Compiler::compile_condition(const goos::Object& condition, Env* env, b
       auto fas = first.as_symbol();
 
       // if there's a not, we can just try again to get an optimization with the invert flipped.
-      if (fas->name == "not") {
+      if (fas == "not") {
         if (!pair_cdr(rest).is_empty_list()) {
           throw_compiler_error(condition, "A condition with \"not\" can have only one argument");
         }
@@ -62,7 +62,7 @@ Condition Compiler::compile_condition(const goos::Object& condition, Env* env, b
       }
 
       auto& conditions = invert ? conditions_inverted : conditions_normal;
-      auto nc_kv = conditions.find(fas->name);
+      auto nc_kv = conditions.find(fas.name_ptr);
 
       if (nc_kv != conditions.end()) {
         // it is an optimizable condition!
@@ -290,7 +290,7 @@ Val* Compiler::compile_cond(const goos::Object& form, const goos::Object& rest,
 }
 
 Val* Compiler::compile_and_or(const goos::Object& form, const goos::Object& rest, Env* env) {
-  std::string op_name = form.as_pair()->car.as_symbol()->name;
+  std::string op_name = form.as_pair()->car.as_symbol().name_ptr;
   bool is_and = false;
   if (op_name == "and") {
     is_and = true;