Allow CXX and CPPFLAGS override

Makefile

@@ -1,5 +1,5 @@
-CXX=c++
-CPPFLAGS=	-Wall 				\
+CXX ?= c++
+CPPFLAGS ?=	-Wall 				\
 		-Wextra				\
 		-pipe				\
 		-Wmissing-declarations		\
@@ -9,17 +9,17 @@ CPPFLAGS=	-Wall 				\
 
 LDFLAGS=-lncursesw -Wl,-z,relro,-z,now
 
-SOURCES=main.cpp	\
-	chess.cpp	\
-	bishop.cpp	\
-	rook.cpp	\
-	queen.cpp	\
-	king.cpp	\
-	knight.cpp	\
-	pawn.cpp
+SOURCES =	main.cpp	\
+		chess.cpp	\
+		bishop.cpp	\
+		rook.cpp	\
+		queen.cpp	\
+		king.cpp	\
+		knight.cpp	\
+		pawn.cpp
 
-OBJECTS=$(SOURCES:.cpp=.o)
-EXECUTABLE=chess
+OBJECTS = $(SOURCES:.cpp=.o)
+EXECUTABLE = chess
 
 all: $(SOURCES) $(EXECUTABLE)