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...
C:\Users\User>e:install-avr-tools
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"
C:\Users\User>