Official KB article 2927432
Compiler and CRT
VS 2013 Update 2 includes a new version of the C++ compiler (18.00.30501.0). There's no new C/C++ Runtime--it still uses CRT version 12.0.21005.1 from VS 2013 RTM), but there are updated remote debugging tools packages.
This compiler update includes a new /arch:AVX2 compiler switch.
Windows phone: VS 2013 Update 2 includes the Windows Phone 8.1 SDK.