With WINAVR becoming unmaintained, various people including myself are starting to think that the easiest way of getting a basic set of avr-gcc tools installed on your Windows system is to install Arduino, and use the tools that it includes. But they're buried rather deeply, and a bit of a pain to get to. So I wrote this batch script to go out and look at your Windows (XP, 7, 8, 10) system, find the Arduino tools (1.0.x, 1.6.5+, 1.8.x), and sticks them in the search path for that "Command Prompt" session. It gets avrdude too. It doesn't copy or actually install anything, so it's pretty quick. Now, command-line access to the bare compiler isn't a particularly wonderful development environment, but it might be good for a quick start...
No avr-gcc currently installed. At least one Arduino install found.
Looks like C:\Program Files\Arduino1.8.0 has version avr-gcc.exe (GCC) 4.9.2 Use C:\Program Files\Arduino1.8.0 ? [y/n]>y Found avr-gcc Checking tool versions
avr-gcc (GCC) 4.9.2 Copyright (C) 2014 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
avrdude: Version 6.3, compiled on Dec 16 2016 at 13:33:19 Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/ Copyright (c) 2007-2014 Joerg Wunsch System wide configuration file is "C:\Program Files\Arduino1.8.0\hardware\tools\avr\etc\avrdude.conf"