Add a base makefile for 64 bit only builds.

This makefile specifies a configuration that only starts a 64 bit
zygote (as opposed to both 64/32, as standard 64 bit builds do).
It should be inherited by products that only supports 64 bit apps.

Bug: 72810053
Test: Manual, using product in https://android-review.googlesource.com/608276
Change-Id: Ib88eccf8d4c575bfd93d6edb130348aeca4ae3f8

target/product/core_64_bit_only.mk

@@ -0,0 +1,30 @@
+#
+# Copyright (C) 2014 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.
+#
+
+# Inherit from this product for devices that support only 64-bit apps using:
+# $(call inherit-product, $(SRC_TARGET_DIR)/product/core_64_bit_only.mk)
+# The inheritance for this must come before the inheritance chain that leads
+# to core_minimal.mk.
+
+# Copy the 64-bit zygote startup script
+PRODUCT_COPY_FILES += system/core/rootdir/init.zygote64.rc:root/init.zygote64.rc
+
+# Set the zygote property to select the 64-bit script.
+# This line must be parsed before the one in core_minimal.mk
+PRODUCT_DEFAULT_PROPERTY_OVERRIDES += ro.zygote=zygote64
+
+TARGET_SUPPORTS_32_BIT_APPS := false
+TARGET_SUPPORTS_64_BIT_APPS := true