Properly handle CFLAGS et al

Makefile

@@ -2,6 +2,8 @@ PREFIX ?= /local
 EXEC_PREFIX ?= $(PREFIX)
 BINDIR ?= $(EXEC_PREFIX)/bin
 
+CFLAGS ?= -O3 -Wall -Wextra -pedantic
+
 .SUFFIXES:
 .SUFFIXES: .inc .txt
 
@@ -31,7 +33,7 @@ TILES = player_stand_tile.inc \
 all: $(NAME)
 
 $(NAME): $(NAME).c $(TILES)
-	$(CC) -O3 -Wall -Wextra -Werror -pedantic -o $@ $< -ldisplay
+	$(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) -o $@ $< -ldisplay
 
 .txt.inc:
 	./tile_compiler.py $< > $@