Fix gitignore problem

nemu/build/obj/cpu/exec/relop.d

-build/obj/cpu/exec/relop.o: src/cpu/exec/relop.cc include/common.h \
- include/debug.h include/common.h include/macro.h include/cpu/relop.h

nemu/build/obj/cpu/exec/special.d

-build/obj/cpu/exec/special.o: src/cpu/exec/special.cc include/cpu/exec.h \
- include/nemu.h include/common.h include/debug.h include/macro.h \
- include/memory/memory.h include/common.h include/cpu/reg.h \
- include/cpu/decode.h include/cpu/rtl.h include/util/c_op.h \
- include/cpu/relop.h include/cpu/rtl-wrapper.h include/macro.h \
- include/monitor/monitor.h

nemu/build/obj/cpu/exec/system.d

-build/obj/cpu/exec/system.o: src/cpu/exec/system.cc include/cpu/exec.h \
- include/nemu.h include/common.h include/debug.h include/macro.h \
- include/memory/memory.h include/common.h include/cpu/reg.h \
- include/cpu/decode.h include/cpu/rtl.h include/util/c_op.h \
- include/cpu/relop.h include/cpu/rtl-wrapper.h include/macro.h

nemu/build/obj/cpu/intr.d

-build/obj/cpu/intr.o: src/cpu/intr.cc include/cpu/exec.h include/nemu.h \
- include/common.h include/debug.h include/macro.h include/memory/memory.h \
- include/common.h include/cpu/reg.h include/cpu/decode.h \
- include/cpu/rtl.h include/util/c_op.h include/cpu/relop.h \
- include/cpu/rtl-wrapper.h include/macro.h include/memory/mmu.h

nemu/build/obj/cpu/reg.d

-build/obj/cpu/reg.o: src/cpu/reg.cc include/nemu.h include/common.h \
- include/debug.h include/macro.h include/memory/memory.h include/common.h \
- include/cpu/reg.h

nemu/build/obj/device/device.d

-build/obj/device/device.o: src/device/device.cc include/common.h \
- include/debug.h include/common.h include/macro.h

nemu/build/obj/device/io/mmio.d

-build/obj/device/io/mmio.o: src/device/io/mmio.cc include/common.h \
- include/debug.h include/common.h include/macro.h include/device/mmio.h

nemu/build/obj/device/io/port-io.d

-build/obj/device/io/port-io.o: src/device/io/port-io.cc include/common.h \
- include/debug.h include/common.h include/macro.h \
- include/device/port-io.h

nemu/build/obj/device/keyboard.d

-build/obj/device/keyboard.o: src/device/keyboard.cc \
- include/device/port-io.h include/common.h include/debug.h \
- include/common.h include/macro.h include/monitor/monitor.h

nemu/build/obj/device/serial.d

-build/obj/device/serial.o: src/device/serial.cc include/common.h \
- include/debug.h include/common.h include/macro.h \
- include/device/port-io.h