Fixed invalid Makefile.

os/ass4/Makefile

-PROG	= philosophers
+PROG	= ass4
 
 CC		= gcc
-CFLAGS	= -ansi -Wall -Wextra -O3 -pthread
-OFILES	= host.o
+CFLAGS	= -std=c99 -pedantic -Wall -Wextra -D_GNU_SOURCE # -D_POSIX_SOURCE
+LFLAGS	= -lpthread
+OFILES	= main.o
 RM		= rm -f
 
+ifdef DEBUG
+	CFLAGS +=-ggdb
+else
+	CFLAGS +=-O3
+endif
+
 $(PROG): $(OFILES)
-	$(CC) -o $(PROG) $(OFILES) $(CFLAGS)
+	$(CC) $(CFLAGS) $(LFLAGS) -o $@ $(OFILES)
 
 %.o: %.c
-	$(CC) -c $< $(CFLAGS)
+	$(CC) $(CFLAGS) -o $@ -c $<
 
 clean:
-	$(RM) *.o $(PROG)
+	$(RM) $(OFILES) $(PROG)