title: Makefile says that variable is empty but it's not
body: <p>I'm trying to create makefile with following content:</p>
  
  <pre><code>$(CXX)=g++
  $(SRC)=../src
  $(INCL)=../include
  all: cpu ram temperature swap statusshooter
      $(CXX) main.cpp cpu.o ram.o temperature.o swap.o statusshooter.o -o main.o -I$(INCL) -Ofast -Wall -lyaml-cpp -lglog -lpqxx -lpq
  cpu:
      $(CXX) -c $(SRC)/CCpu.cpp -o cpu.o -Ofast -Wall 
  ram:
      $(CXX) -c $(SRC)/CRam.cpp -o ram.o -Ofast -Wall 
  temperature:
      $(CXX) -c $(SRC)/CTemperature.cpp -o temperature.o -Ofast -Wall
  swap:
      $(CXX) -c $(SRC)/CSwap.cpp -o swap.o -Ofast -Wall  
  statusshooter:
      $(CXX) -c $(SRC)/CStatusShooter.cpp -o statusshooter.o -Ofast -Wall  
  </code></pre>
  
  <p>Executing that makefile with:
  <code>make CXX=g++-4.7</code> throws following error:</p>
  
  <pre><code>makefile:2: *** empty variable name.  Stop.
  </code></pre>
  
  <p>How to resolve this?</p>