Fix #3497: Add support for compiling in g++ 4.4 and 4.5

- Removed uses of lambda expressions

- Added custom defines for constexpr and nullptr

- Removed trailing comma of last value from generated enums

include/flatbuffers/util.h

@@ -38,6 +38,8 @@
 #include <limits.h>
 #endif
 
+#include "flatbuffers/flatbuffers.h"
+
 namespace flatbuffers {
 
 // Convert an integer or floating point value to a string.
@@ -68,7 +70,7 @@ template<> inline std::string NumToString<double>(double t) {
   auto p = s.find_last_not_of('0');
   if (p != std::string::npos) {
     s.resize(p + 1);  // Strip trailing zeroes.
-    if (s.back() == '.')
+    if (s[s.size() - 1] == '.')
       s.erase(s.size() - 1, 1);  // Strip '.' if a whole number.
   }
   return s;
@@ -197,8 +199,8 @@ inline std::string StripFileName(const std::string &filepath) {
 inline std::string ConCatPathFileName(const std::string &path,
                                       const std::string &filename) {
   std::string filepath = path;
-  if (path.length() && path.back() != kPathSeparator &&
-                       path.back() != kPosixPathSeparator)
+  if (path.length() && path[path.size() - 1] != kPathSeparator &&
+                       path[path.size() - 1] != kPosixPathSeparator)
     filepath += kPathSeparator;
   filepath += filename;
   return filepath;