Add Rust support to Soong.

Adds support to Soong for building rust modules. This currently only
supports x86_64 device and x86 linux host targets. The functionality
is sufficient to build crosvm.

Bug: 136189233
Test: Test module builds.
Test: crosvm builds.
Change-Id: I6ea04615834a6d673578ab10ea1a2eb04259fe09

rust/prebuilt.go

@@ -0,0 +1,65 @@
+// Copyright 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 rust
+
+import (
+	"android/soong/android"
+)
+
+func init() {
+	android.RegisterModuleType("rust_prebuilt_dylib", PrebuiltDylibFactory)
+}
+
+type PrebuiltProperties struct {
+	// path to the prebuilt file
+	Srcs []string `android:"path,arch_variant"`
+}
+
+type prebuiltLibraryDecorator struct {
+	*libraryDecorator
+	Properties PrebuiltProperties
+}
+
+var _ compiler = (*prebuiltLibraryDecorator)(nil)
+
+func PrebuiltDylibFactory() android.Module {
+	module, _ := NewPrebuiltDylib(android.HostAndDeviceSupported)
+	return module.Init()
+}
+
+func NewPrebuiltDylib(hod android.HostOrDeviceSupported) (*Module, *prebuiltLibraryDecorator) {
+	module, library := NewRustLibrary(hod)
+	library.BuildOnlyDylib()
+	library.setDylib()
+	prebuilt := &prebuiltLibraryDecorator{
+		libraryDecorator: library,
+	}
+	module.compiler = prebuilt
+	module.AddProperties(&library.Properties)
+	return module, prebuilt
+}
+
+func (prebuilt *prebuiltLibraryDecorator) compilerProps() []interface{} {
+	return append(prebuilt.baseCompiler.compilerProps(),
+		&prebuilt.Properties)
+}
+
+func (prebuilt *prebuiltLibraryDecorator) compile(ctx ModuleContext, flags Flags, deps PathDeps) android.Path {
+	srcPath := srcPathFromModuleSrcs(ctx, prebuilt.Properties.Srcs)
+
+	prebuilt.unstrippedOutputFile = srcPath
+
+	return srcPath
+}