use C++ standard c++14

config.m4

@@ -39,11 +39,11 @@ if test "$PHP_V8JS" != "no"; then
 
 
   AC_CACHE_CHECK(for C standard version, ac_cv_v8_cstd, [
-    ac_cv_v8_cstd="c++11"
+    ac_cv_v8_cstd="c++14"
     old_CPPFLAGS=$CPPFLAGS
     AC_LANG_PUSH([C++])
     CPPFLAGS="-std="$ac_cv_v8_cstd
-    AC_RUN_IFELSE([AC_LANG_SOURCE([[int main() { return 0; }]])],[],[ac_cv_v8_cstd="c++0x"],[])
+    AC_RUN_IFELSE([AC_LANG_SOURCE([[int main() { return 0; }]])],[],[ac_cv_v8_cstd="c++1y"],[])
     AC_LANG_POP([C++])
     CPPFLAGS=$old_CPPFLAGS
   ]);