adding simple makefile to build door challenge

.gitignore

-*.out
+/challenge/*.o
+/doorchallenge

Makefile

+TARGET=doorchallenge
+
+CC:=gcc
+LD:=$(CC)
+
+LDLIBS=
+LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro
+CFLAGS=-Wall \
+	-Wextra \
+	-Winit-self \
+	-Wuninitialized \
+	-Wfloat-equal \
+	-Wint-to-pointer-cast \
+	-pedantic \
+	-O2 \
+	-fstack-protector-strong
+
+all: $(TARGET)
+
+$(TARGET): challenge/challenge.o
+	$(LD) $(LDFLAGS) -o $@ $^ $(LDLIBS)
+
+challenge/%.o: challenge/%.c
+	$(CC) $(CFLAGS) -c $< -o $@
+
+clean:
+	$(RM) -rf challenge/*.o $(TARGET)