fix how to compile with SDL2, added SDL2_CONFIG to var.mk

Both 2014/maffiodo1 and 2018/giles now use ${SDL2_CONFIG}
to compile with SDL2.

2014/maffiodo1/Makefile

@@ -105,7 +105,7 @@ CDEFINE=
 #CINCLUDE= -include stdio.h
 #CINCLUDE= -include stdlib.h -include stdio.h
 #CINCLUDE= -I ${X11_INCDIR}
-CINCLUDE= -I ${HOMEBREW_PREFIX}/include/SDL2
+CINCLUDE= `${SDL2_CONFIG} --cflags`
 
 # Optimization
 #
@@ -129,7 +129,7 @@ CFLAGS= ${CSTD} ${CWARN} ${ARCH} ${CDEFINE} ${CINCLUDE} ${OPT}
 #LIBS=
 #LIBS= -lm
 #LIBS= -L ${X11_LIBDIR} -lX11
-LIBS= -L ${HOMEBREW_PREFIX}/lib -lSDL2
+LIBS= `${SDL2_CONFIG} --libs`
 
 # C compiler to use
 #