For gcc 4.8.4 you need to use -std=c++1y in later versions, looks like starting with 5.2 you can use -std=c++14.
If we look at the gcc online documents we can find the manuals for each version of gcc and we can see by going to Dialect options for 4.9.3 under the GCC 4.9.3 manual it says:
‘c++1y’
The next revision of the ISO C++ standard, tentatively planned for 2014. Support is highly experimental, and will almost certainly change in incompatible ways in future releases.
So up till 4.9.3 you had to use -std=c++1y while the gcc 5.2 options say:
‘c++14’ ‘c++1y’
The 2014 ISO C++ standard plus amendments. The name ‘c++1y’ is deprecated.
It is not clear to me why this is listed under Options Controlling C Dialect but that is how the documents are currently organized.