Toward using a more modern C++ compiler:

Raspberry Pi -- Install GCC 4.9 and compile C++14 programs

by Sol

From the article:

...  I will show you next how to install only GCC 4.9 and his dependencies from Jessie and keep Wheezy as the default source for all the other packages. I’ve tested the next steps on a Raspberry Pi revision B+, but it should work on older models too...