add basic resolution of enums to llvm types

- pass ctx to codegen
 - add better type solver error for unhandled nodes

examples/hello.ry

@@ -1,16 +1,13 @@
 // import std;
 
-struct B {
-    field i32
+enum B {
+    a
+    b
+    c
 }
 
-struct Awoo {
-    b B
-    other_field i32
-}
-
-fn test_function() Awoo {
-    return 1;
+fn test_function() B {
+    return B.a;
 }
 
 fn multwo(num: i32, double_flag: bool) i32 {