Implement vendor snapshot

Vendor snapshot can be captured with "m dist vendor-snapshot". With
vendor snapshot and vndk snapshot, older version of /vendor and newer
version of /system will be able to be built together by setting
BOARD_VNDK_VERSION to past vendor's version.

Only vendor modules under AOSP are to be captured. In detail, modules
under following directories are ignored:
- cts/
- device/
- external/clang/
- external/llvm/
- hardware/, except for:
    - interfaces/, libhardware/, libhardware_legacy/, ril/
- vendor/

Bug: 65377115
Test: m dist vendor-snapshot
Change-Id: Ib5859e409f8ab281ca137cae21e9ea08abd8a0b1

core/tasks/vendor_snapshot.mk

@@ -0,0 +1,34 @@
+# Copyright (C) 2020 The Android Open Source Project
+#
+# 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
+#
+#      http://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.
+
+current_makefile := $(lastword $(MAKEFILE_LIST))
+
+# BOARD_VNDK_VERSION must be set to 'current' in order to generate a vendor snapshot.
+ifeq ($(BOARD_VNDK_VERSION),current)
+
+.PHONY: vendor-snapshot
+vendor-snapshot: $(SOONG_VENDOR_SNAPSHOT_ZIP)
+
+$(call dist-for-goals, vendor-snapshot, $(SOONG_VENDOR_SNAPSHOT_ZIP))
+
+else # BOARD_VNDK_VERSION is NOT set to 'current'
+
+.PHONY: vendor-snapshot
+vendor-snapshot: PRIVATE_MAKEFILE := $(current_makefile)
+vendor-snapshot:
+	$(call echo-error,$(PRIVATE_MAKEFILE),\
+		"CANNOT generate Vendor snapshot. BOARD_VNDK_VERSION must be set to 'current'.")
+	exit 1
+
+endif # BOARD_VNDK_VERSION

core/tasks/vndk.mk

@@ -43,8 +43,9 @@ endif # BOARD_VNDK_VERSION
 ifneq (,$(error_msg))
 
 .PHONY: vndk
+vndk: PRIVATE_MAKEFILE := $(current_makefile)
 vndk:
-	$(call echo-error,$(current_makefile),$(error_msg))
+	$(call echo-error,$(PRIVATE_MAKEFILE),$(error_msg))
 	exit 1
 
 endif