title: tell if make is running on windows or linux
body: <p>Is there a way to know in makefiles if GNU make is running on a linux OS or a windows OS?</p>
  
  <p>I've built a bash script that generates a makefile for building my app and it works fine on my Debian machine. I want to try to build it on MinGW/MSYS, but the problem is that I have to build and run some test programs that check errors in source code, and to run it on Windows, I must add the .exe suffix.</p>