drop code for handling undefines

Since 0.12 dropped support for undefines, we can remove the code to
support it as well.

src/cps/loader.cpp

@@ -279,17 +279,11 @@ namespace cps::loader {
 
     } // namespace
 
-    Define::Define(std::string name_) : name{std::move(name_)}, value{}, define{true} {};
-    Define::Define(std::string name_, std::string value_)
-        : name{std::move(name_)}, value{std::move(value_)}, define{true} {};
-    Define::Define(std::string name_, bool define_) : name{std::move(name_)}, value{}, define{define_} {};
-
-    bool Define::is_undefine() const { return !define; }
-
-    bool Define::is_define() const { return define && value.empty(); }
+    Define::Define(std::string name_) : name{std::move(name_)}, value{std::nullopt} {};
+    Define::Define(std::string name_, std::string value_) : name{std::move(name_)}, value{std::move(value_)} {};
 
     std::string Define::get_name() const { return name; }
-    std::string Define::get_value() const { return value; }
+    std::optional<std::string> Define::get_value() const { return value; }
 
     Configuration::Configuration() = default;
     Configuration::Configuration(LangValues cflags) : compile_flags{std::move(cflags)} {};

src/cps/loader.hpp

@@ -47,17 +47,13 @@ namespace cps::loader {
       public:
         Define(std::string name);
         Define(std::string name, std::string value);
-        Define(std::string name, bool define);
 
-        bool is_undefine() const;
-        bool is_define() const;
         std::string get_name() const;
-        std::string get_value() const;
+        std::optional<std::string> get_value() const;
 
       private:
         std::string name;
-        std::string value;
-        bool define;
+        std::optional<std::string> value;
     };
 
     using LangValues = std::unordered_map<KnownLanguages, std::vector<std::string>>;

src/cps/printer.cpp

@@ -40,12 +40,10 @@ namespace cps::printer {
             if (auto && f = r.definitions.find(loader::KnownLanguages::c);
                 f != r.definitions.end() && !f->second.empty()) {
                 auto && transformer = [](auto && d) {
-                    if (d.is_define()) {
-                        return fmt::format("-D{}", d.get_name());
-                    } else if (d.is_undefine()) {
-                        return fmt::format("-U{}", d.get_name());
+                    if (auto && v = d.get_value()) {
+                        return fmt::format("-D{}={}", d.get_name(), v.value());
                     } else {
-                        return fmt::format("-D{}={}", d.get_name(), d.get_value());
+                        return fmt::format("-D{}", d.get_name());
                     }
                 };
                 args.reserve(args.size() + f->second.size());