hidden symbols as decls front-appended to parser-result

(not really front-appended but decl_codegen() won't care if it's called twice on different declaration lists).

Hidden symbols are now 'appended' (see above) to struct decl* parser_result so that when it comes to decl_codegen(), all necessary symbols, including hidden symbols, will be in the list(s), with no need to look through the symbol table several times to check for symbols that may not even be in the table (if no string literals are ever used for instance).

svhawkins / B-Minor-Compiler

hidden symbols as decls front-appended to parser-result #4