title: Environment variables in Windows makefiles
body: <p>I have the following in a <code>makefile</code> I'm using with <code>mingw32-make</code></p>
  
  <pre><code>ifeq (%PROCESSOR_ARCHITECTURE%,AMD64)
      ARCH ?= 64
  else
      ARCH ?= 32
  endif
  </code></pre>
  
  <p>For some reason <code>PROCESSOR_ARCHITECTURE</code> isn't returning the correct value. I've tried <code>$(PROCESSOR_ARCHITECTURE)</code> and <code>$(%PROCESSOR_ARCHITECTURE%)</code> as well. Not sure what's wrong here.</p>