Add busybox and flashcard support

Change-Id: Id572498f3282f7b7a28b3a7afd80d67146645c21
diff --git a/Makefile b/Makefile
index 053db2a..f53324f 100644
--- a/Makefile
+++ b/Makefile
@@ -44,6 +44,7 @@
 include $(ROOTDIR)/board/partition-table.mk
 
 include $(ROOTDIR)/build/img2simg.mk
+include $(ROOTDIR)/build/busybox.mk
 include $(ROOTDIR)/build/prereqs.mk
 include $(ROOTDIR)/build/rootfs.mk
 include $(ROOTDIR)/build/docker.mk
@@ -52,6 +53,7 @@
 
 include $(ROOTDIR)/board/bootloader.mk
 -include $(ROOTDIR)/board/sdcard.mk
+-include $(ROOTDIR)/board/flashcard.mk
 -include $(ROOTDIR)/board/recovery.mk
 
 clean::
diff --git a/busybox.mk b/busybox.mk
new file mode 100644
index 0000000..2a53afa
--- /dev/null
+++ b/busybox.mk
@@ -0,0 +1,37 @@
+# Copyright 2019 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+ifeq ($(ROOTDIR),)
+$(error $$ROOTDIR IS NOT DEFINED -- don\'t forget to source setup.sh)
+endif
+
+include $(ROOTDIR)/build/preamble.mk
+
+BUSYBOX_WORK_DIR := $(PRODUCT_OUT)/obj/busybox
+
+busybox: $(PRODUCT_OUT)/busybox
+$(PRODUCT_OUT)/busybox:
+	mkdir -p $(BUSYBOX_WORK_DIR)
+	+make -C $(ROOTDIR)/tools/busybox O=$(BUSYBOX_WORK_DIR) enterprise_defconfig
+	+make -C $(ROOTDIR)/tools/busybox O=$(BUSYBOX_WORK_DIR)
+	cp $(BUSYBOX_WORK_DIR)/busybox $(PRODUCT_OUT)/busybox
+
+targets::
+	@echo "busybox - embedded swiss-army knife"
+
+clean::
+	rm -rf $(BUSYBOX_WORK_DIR)
+	rm -rf $(PRODUCT_OUT)/busybox
+
+.PHONY:: busybox
diff --git a/prereqs.mk b/prereqs.mk
index f429017..c6c7397 100644
--- a/prereqs.mk
+++ b/prereqs.mk
@@ -27,7 +27,10 @@
 	binfmt-support \
 	ca-certificates \
 	cdbs \
+	crossbuild-essential-arm64 \
+	crossbuild-essential-armhf \
 	coreutils \
+	cpio \
 	curl \
 	debhelper \
 	debian-archive-keyring \