Pass --target and --sysroot to dtc as CPPFLAGS
This is necessary for the depfiles to be correct when cross-compiling.
diff --git a/Makefile b/Makefile
index 8a9113e..e028102 100644
--- a/Makefile
+++ b/Makefile
@@ -528,7 +528,7 @@
DTC_MAKE_ARGS=-I$(SRC_PATH)/dtc VPATH=$(SRC_PATH)/dtc -C dtc V="$(V)" LIBFDT_srcdir=$(SRC_PATH)/dtc/libfdt
DTC_CFLAGS=$(CFLAGS) $(QEMU_CFLAGS)
-DTC_CPPFLAGS=-I$(BUILD_DIR)/dtc -I$(SRC_PATH)/dtc -I$(SRC_PATH)/dtc/libfdt
+DTC_CPPFLAGS=-I$(BUILD_DIR)/dtc -I$(SRC_PATH)/dtc -I$(SRC_PATH)/dtc/libfdt $(filter --target% --sysroot%,$(QEMU_CFLAGS))
.PHONY: dtc/all
dtc/all: .git-submodule-status dtc/libfdt dtc/tests
