Re-apply the Clang/C+11 fix for JSBSim

Hopefully an equivalent change will occur upstream before the next
JSBsim sync.

diff --git a/src/FDM/JSBSim/input_output/string_utilities.h b/src/FDM/JSBSim/input_output/string_utilities.h
index d25e258b351beab95ae390405a7ab3bce70e9d98..9bb120b04bdcf3b8a9346b38754e09968379e5e4 100644 (file)
--- a/src/FDM/JSBSim/input_output/string_utilities.h
+++ b/src/FDM/JSBSim/input_output/string_utilities.h
@@ -73,10 +73,14 @@ CLASS DECLARATION
   extern std::string& to_lower(std::string& str);
   extern bool is_number(const std::string& str);
   std::vector <std::string> split(std::string str, char d);
-/* Comment out to_string functions when they are defined already - C++ 11 defines these */
+
+// libc++ has these as built-ins for all C++ language versions
+#if !defined(_LIBCPP_VERSION)
   extern std::string to_string(int);
   extern std::string to_string(double);
   extern std::string to_string(float);
+#endif
+
   extern std::string replace(std::string str, const std::string& old, const std::string& newstr);
 #else
   #include <cctype>