title: Simple way to pass variables to CFLAGS in a make file
body: <p>I have a Makefile which looks like below. I use <code>ifeq</code> to add variables to compiler flags.  </p>
  
  <pre><code>ABC=1
  XYZ=1
  
  ifeq ($(ABC),1)
  CFLAGS+= -DABC
  endif
  
  ifeq ($(XYZ),1)
  CFLAGS+= -DXYZ
  endif
  
  ...
  </code></pre>
  
  <p>Is there a cleaner way to add all variables to CFLAGS instead of using ifeq for all?</p>