option_types.hh: fix unfulfilled dependencies of the header

src/option_types.hh

@@ -9,6 +9,7 @@
 #include "option.hh"
 #include "ranges.hh"
 #include "string.hh"
+#include "string_utils.hh"
 #include "units.hh"
 
 #include <tuple>
@@ -235,6 +236,8 @@ inline bool option_add(WorstMatch, StringView)
     throw runtime_error("no add operation supported for this option type");
 }
 
+class Context;
+
 inline void option_update(WorstMatch, const Context&)
 {
     throw runtime_error("no update operation supported for this option type");