Create sysprop_library soong module

A newly introduced sysprop_library soong module will generate a
java_sdk_library and a cc_library from .sysprop description files.
Both Java modules and C++ modules can link against sysprop_library
module, thus giving consistency for using generated sysprop API.

As Java controls accessibility of Internal / System properties with
@hide and @SystemApi, 2 different header files will be created. And
build system will selectively expose depending on the property owner
and the place where the client libraries go into.

Bug: 80125326
Bug: 122170616
Test: 1) Create sysprop_library module.
Test: 2) Create empty txt files under prebuilts/sdk.
Test: 3) Create api directory, make update-api, and see changes.
Test: 4) Try to link against sysprop_library with various clients.
Test: 5) Soc_specific, Device_specific, Product_specific, recovery flags
work as intended.
Change-Id: I78dc5780ccfbb4b69e5c61dec26b94e92d43c333

cc/sysprop.go

@@ -0,0 +1,47 @@
+// Copyright (C) 2019 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.
+
+package cc
+
+import (
+	"sync"
+
+	"android/soong/android"
+)
+
+type syspropLibraryInterface interface {
+	CcModuleName() string
+}
+
+var (
+	syspropImplLibrariesKey  = android.NewOnceKey("syspropImplLibirares")
+	syspropImplLibrariesLock sync.Mutex
+)
+
+func syspropImplLibraries(config android.Config) map[string]string {
+	return config.Once(syspropImplLibrariesKey, func() interface{} {
+		return make(map[string]string)
+	}).(map[string]string)
+}
+
+// gather list of sysprop libraries
+func SyspropMutator(mctx android.BottomUpMutatorContext) {
+	if m, ok := mctx.Module().(syspropLibraryInterface); ok {
+		syspropImplLibraries := syspropImplLibraries(mctx.Config())
+		syspropImplLibrariesLock.Lock()
+		defer syspropImplLibrariesLock.Unlock()
+
+		syspropImplLibraries[mctx.ModuleName()] = m.CcModuleName()
+	}
+}