Make Makefile more useful for cross-compiling

Makefile

@@ -2,6 +2,11 @@
 MESA_INCLUDE ?= /home/cubox/mesa/include
 MESA_LIB ?= /home/cubox/mesa/lib
 
+CC = $(GCCPREFIX)gcc
+CXX = $(GCCPREFIX)g++
+LD = $(GCCPREFIX)ld
+AR = $(GCCPREFIX)ar
+
 INCDIR=-g -O -I./Common -I${MESA_INCLUDE} -DMESA_EGL_NO_X11_HEADERS
 LIBS=-L${MESA_LIB} -lGLESv2 -lEGL -lm
 
@@ -46,31 +51,31 @@ clean:
 	find . -name "CH??_*" | xargs rm -f
 
 ./Hello_Triangle/CH02_HelloTriangle: ${COMMONSRC} ${COMMONHDR} ${CH02SRC}
-	gcc ${COMMONSRC} ${CH02SRC} -o $@ ${INCDIR} ${LIBS}
+	${CC} ${COMMONSRC} ${CH02SRC} -o $@ ${INCDIR} ${LIBS}
 ./Simple_VertexShader/CH08_SimpleVertexShader: ${COMMONSRC} ${COMMONHDR} ${CH08SRC}
-	gcc ${COMMONSRC} ${CH08SRC} -o ./$@ ${INCDIR} ${LIBS}
+	${CC} ${COMMONSRC} ${CH08SRC} -o ./$@ ${INCDIR} ${LIBS}
 ./Simple_Texture2D/CH09_SimpleTexture2D: ${COMMONSRC} ${COMMONHDR} ${CH09SRC1}
-	gcc ${COMMONSRC} ${CH09SRC1} -o ./$@ ${INCDIR} ${LIBS}
+	${CC} ${COMMONSRC} ${CH09SRC1} -o ./$@ ${INCDIR} ${LIBS}
 ./MipMap2D/CH09_MipMap2D: ${COMMONSRC} ${COMMONHDR} ${CH09SRC2}
-	gcc ${COMMONSRC} ${CH09SRC2} -o ./$@ ${INCDIR} ${LIBS}
+	${CC} ${COMMONSRC} ${CH09SRC2} -o ./$@ ${INCDIR} ${LIBS}
 ./Simple_TextureCubemap/CH09_TextureCubemap: ${COMMONSRC} ${COMMONHDR} ${CH09SRC3}
-	gcc ${COMMONSRC} ${CH09SRC3} -o ./$@ ${INCDIR} ${LIBS}
+	${CC} ${COMMONSRC} ${CH09SRC3} -o ./$@ ${INCDIR} ${LIBS}
 ./TextureWrap/CH09_TextureWrap: ${COMMONSRC} ${COMMONHDR} ${CH09SRC4}
-	gcc ${COMMONSRC} ${CH09SRC4} -o ./$@ ${INCDIR} ${LIBS}
+	${CC} ${COMMONSRC} ${CH09SRC4} -o ./$@ ${INCDIR} ${LIBS}
 ./MultiTexture/CH10_MultiTexture: ${COMMONSRC} ${COMMONHDR} ${CH10SRC}
-	gcc ${COMMONSRC} ${CH10SRC} -o ./$@ ${INCDIR} ${LIBS}
+	${CC} ${COMMONSRC} ${CH10SRC} -o ./$@ ${INCDIR} ${LIBS}
 ./Multisample/CH11_Multisample: ${COMMONSRC} ${COMMONHDR} ${CH11SRC}
-	gcc ${COMMONSRC} ${CH11SRC} -o ./$@ ${INCDIR} ${LIBS}
+	${CC} ${COMMONSRC} ${CH11SRC} -o ./$@ ${INCDIR} ${LIBS}
 ./Stencil_Test/CH11_Stencil_Test: ${COMMONSRC} ${COMMONHDR} ${CH11SRC2}
-	gcc ${COMMONSRC} ${CH11SRC2} -o ./$@ ${INCDIR} ${LIBS}
+	${CC} ${COMMONSRC} ${CH11SRC2} -o ./$@ ${INCDIR} ${LIBS}
 ./Noise3D/CH13_Noise3D: ${COMMONSRC} ${COMMONHDR} ${CH13SRC1}
-	gcc ${COMMONSRC} ${CH13SRC1} -o ./$@ ${INCDIR} ${LIBS}
+	${CC} ${COMMONSRC} ${CH13SRC1} -o ./$@ ${INCDIR} ${LIBS}
 ./ParticleSystem/CH13_ParticleSystem: ${COMMONSRC} ${COMMONHDR} ${CH13SRC2}
-	gcc ${COMMONSRC} ${CH13SRC2} -o ./$@ ${INCDIR} ${LIBS}
+	${CC} ${COMMONSRC} ${CH13SRC2} -o ./$@ ${INCDIR} ${LIBS}
 ./Cube/cube: ${COMMONSRC} ${COMMONHDR} ${CUBESRC}
-	gcc ${COMMONSRC} ${CUBESRC} -o ./$@ ${INCDIR} ${LIBS}
+	${CC} ${COMMONSRC} ${CUBESRC} -o ./$@ ${INCDIR} ${LIBS}
 ./CubeVBO/cube_vbo: ${COMMONSRC} ${COMMONHDR} ${CUBEVBOSRC}
-	gcc ${COMMONSRC} ${CUBEVBOSRC} -o ./$@ ${INCDIR} ${LIBS}
+	${CC} ${COMMONSRC} ${CUBEVBOSRC} -o ./$@ ${INCDIR} ${LIBS}
 ./Viewports/viewports: ${COMMONSRC} ${COMMONHDR} ${VIEWPORTSSRC}
-	gcc ${COMMONSRC} ${VIEWPORTSSRC} -o ./$@ ${INCDIR} ${LIBS}
+	${CC} ${COMMONSRC} ${VIEWPORTSSRC} -o ./$@ ${INCDIR} ${LIBS}