Fix gitignore problem

.gitignore

+*.d
+*.o
+*.out
+build

nemu/build/obj/cpu/decode/decode.d

-build/obj/cpu/decode/decode.o: src/cpu/decode/decode.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/cpu/rtl.h

nemu/build/obj/cpu/decode/modrm.d

-build/obj/cpu/decode/modrm.o: src/cpu/decode/modrm.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/cpu/rtl.h

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

-build/obj/cpu/exec/arith.o: src/cpu/exec/arith.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/exec/cc.d

-build/obj/cpu/exec/cc.o: src/cpu/exec/cc.cc include/cpu/rtl.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/util/c_op.h include/cpu/relop.h include/cpu/rtl-wrapper.h \
- include/macro.h

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

-build/obj/cpu/exec/control.o: src/cpu/exec/control.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/cpu/cc.h

nemu/build/obj/cpu/exec/data-mov.d

-build/obj/cpu/exec/data-mov.o: src/cpu/exec/data-mov.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/exec/exec.d

-build/obj/cpu/exec/exec.o: src/cpu/exec/exec.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 \
- src/cpu/exec/all-instr.h

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

-build/obj/cpu/exec/logic.o: src/cpu/exec/logic.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/cpu/cc.h

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

-build/obj/cpu/exec/prefix.o: src/cpu/exec/prefix.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