just use implicit rules so correct variables get used

--- Makefile
+++ Makefile
@@ -1,20 +1,13 @@
-CFLAGS= -Wall -Wshadow -Wwrite-strings -Wsign-compare -Wfloat-equal \
+CFLAGS+= -Wall -Wshadow -Wwrite-strings -Wsign-compare -Wfloat-equal \
 	-Wmissing-noreturn -Wbad-function-cast \
-	-Wmissing-prototypes -Winline -Wredundant-decls -O3
+	-Wmissing-prototypes -Winline -Wredundant-decls
 
 all: pdfcrack
 
 pdfcrack: main.o rc4.o md5.o pdfcrack.o pdfparser.o passwords.o common.o \
 	benchmark.o
-	gcc $(CFLAGS) -o $@ $+
-	strip $@
 
 pdfreader: pdfparser.o pdfreader.o common.o
-	gcc $(CFLAGS) -o $@ $+
-	strip $@
 
 clean:
 	rm -f pdfcrack pdfreader testreader *.o
-
-%.o: %.c
-	gcc $(CFLAGS) -c -o $@ $+