Make build system respect user variables

--- a/Makefile
+++ b/Makefile
@@ -1,42 +1,26 @@
-CLASSDIR := .
-
-# Directories to search for header files
-SEARCHDIRS := -I- -I${CLASSDIR}
-
-
-SYSTYPE :=     $(shell uname)
-
-# C compiler
-
-CC      := g++
-CFLAGS  = -Wall ${SEARCHDIRS} -fno-exceptions -fno-rtti -D_REENTRANT -g
+my_CPPFLAGS = -D_REENTRANT -I.
 
 %.o : %.c
-	${CC} ${CFLAGS} -c $< -o $@
+	$(CC) -Wall $(CFLAGS) $(my_CPPFLAGS) $(CPPFLAGS) -c $< -o $@
 
 %.o : %.cc
-	${CC} ${CFLAGS} -c $< -o $@
+	$(CXX) -Wall $(CXXFLAGS) $(my_CPPFLAGS) $(CPPFLAGS) -c $< -o $@
 
 %.o : %.C
-	${CC} ${CFLAGS} -c $< -o $@
+	$(CXX) -Wall $(CXXFLAGS) $(my_CPPFLAGS) $(CPPFLAGS) -c $< -o $@
 
 %.o : %.cpp
-	${CC} ${CFLAGS} -c $< -o $@
+	$(CXX) -Wall $(CXXFLAGS) $(my_CPPFLAGS) $(CPPFLAGS) -c $< -o $@
 
 %.o : %.cxx
-	${CC} ${CFLAGS} -c $< -o $@
+	$(CXX) -Wall $(CXXFLAGS) $(my_CPPFLAGS) $(CPPFLAGS) -c $< -o $@
 
 # C/C++ linker
-
-LINKER    := g++
-LDFLAGS    =
-LOADLIBES := 
-
 .PHONY : all
 all:    elph
 
-elph:  ./elph.o ${CLASSDIR}/motif.o ${CLASSDIR}/GBase.o ${CLASSDIR}/GString.o ${CLASSDIR}/GArgs.o
-	${LINKER} ${LDFLAGS} -o $@ ${filter-out %.a %.so, $^} ${LOADLIBES}
+elph: elph.o motif.o GBase.o GString.o GArgs.o
+	$(CXX) $(LDFLAGS) $(CXXFLAGS) -o $@ $^
 
 # target for removing all object files