cc: add const arrays (wip)

Add a preliminary version of const arrays. It sorta works.
Right now this is limited to function-scope const arrays.

tools/cc.ebnf

@@ -41,10 +41,10 @@ local_var: type symbol initializer?
 local_array: type symbol sized_array* (sized_array | empty_array) initializer? ";"
 empty_array: "[" "]"
 sized_array: "[" array_size "]"
-initializer: "=" (expression | initializer_list)
+?initializer: "=" (expression | initializer_list)
 initializer_list: "{" [init_list_field ("," init_list_field)* ","? ] "}"
 ?init_list_field: "." field "=" expression
-                | expression
+                | prec14_expr
 
 // precedence from https://en.cppreference.com/w/c/language/operator_precedence