Fix Makefile

- Use CXX for C++ code compilation and linking
- Properly allow CXX to be overridden
- Fix file extension in OBJECTS
- Add -c to compilation command
- Link with libm (for cos() and other trigonometry)

Makefile

@@ -1,26 +1,26 @@
 DATADIR?=./
 
-CC=g++ -DDATADIR="\"$(DATADIR)\""
+CXX?=g++
 
-CFLAGS+=-Wall `sdl-config --cflags`
+CXXFLAGS+=-Wall `sdl-config --cflags` -DDATADIR="\"$(DATADIR)\""
 
-LIBS+=-lGL `sdl-config --libs` -lSDL_ttf -lSDL_image -lSDL_mixer
+LIBS+=`sdl-config --libs` -lSDL_ttf -lSDL_image -lSDL_mixer -lGL -lm
 
 SOURCES=main.cpp text.cpp sound.cpp
-OBJECTS=$(SOURCES:.c=.o)
+OBJECTS=$(SOURCES:.cpp=.o)
 
 EXECUTABLE=osgg
 
 all: $(SOURCES) $(EXECUTABLE)
 
 server: server.cpp
-	 $(CC) $(LDFLAGS) server.cpp $(LIBS) -o $@
-	
+	$(CXX) $(CXXFLAGS) $(LDFLAGS) server.cpp $(LIBS) -o $@
+
 $(EXECUTABLE): $(OBJECTS)
-	$(CC) $(LDFLAGS) $(OBJECTS) $(LIBS) -o $@
+	$(CXX) $(LDFLAGS) $(OBJECTS) $(LIBS) -o $@
 
 .cpp.o:
-	$(CC) $(CFLAGS) $< -o $@
+	$(CXX) $(CXXFLAGS) -c $< -o $@
 
 clean:
 	rm -f *.o $(EXECUTABLE)