[core] GCC 4.9 does not provide <codecvt>

platform/default/utf.cpp

@@ -2,14 +2,24 @@
 
 #include <memory>
 #include <locale>
+
+// GCC 4.9 compatibility
+#if !defined(__GNUC__) || __GNUC__ >= 5
 #include <codecvt>
+#else
+#include <boost/locale/encoding_utf.hpp>
+#endif
 
 namespace mbgl {
 namespace util {
 
 std::u16string utf8_to_utf16::convert(std::string const& utf8) {
+#if !defined(__GNUC__) || __GNUC__ >= 5
     std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> converter;
     return converter.from_bytes(utf8);
+#else
+    return boost::locale::conv::utf_to_utf<char16_t>(utf8.c_str(), utf8.c_str() + utf8.size());
+#endif
 }
 
 } // namespace util