Avoid including ranges header under reflective-rapidjson's generator

This works around errors which Clang 11.1.0 has when parsing this header
from GCC 11.1.0. (Yes, at this point the GCC and Clang versions which are
currently in Arch Linux testing are identical.)

conversion/stringconversion.h

@@ -18,7 +18,10 @@
 #include <system_error>
 #include <vector>
 
-#if __cplusplus >= 201709
+#if __cplusplus >= 201709 && !defined(REFLECTIVE_RAPIDJSON_GENERATOR)
+#ifndef CPP_UTILITIES_USE_RANGES
+#define CPP_UTILITIES_USE_RANGES
+#endif
 #include <ranges>
 #endif
 
@@ -65,7 +68,7 @@ CPP_UTILITIES_EXPORT void truncateString(std::string &str, char terminationChar
 
 /// \cond
 namespace Detail {
-#if __cplusplus >= 201709
+#ifdef CPP_UTILITIES_USE_RANGES
 template <class Container>
 using ContainerValueType = typename std::conditional_t<std::ranges::range<Container>,
     std::iterator_traits<std::remove_cvref_t<std::ranges::iterator_t<Container>>>, Container>::value_type;