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
diff --git a/rust/config/x86_64_device.go b/rust/config/x86_64_device.go
new file mode 100644
index 0000000..2aca56a
--- /dev/null
+++ b/rust/config/x86_64_device.go
@@ -0,0 +1,88 @@
+// 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 config
+
+import (
+	"strings"
+
+	"android/soong/android"
+)
+
+var (
+	x86_64RustFlags            = []string{}
+	x86_64ArchFeatureRustFlags = map[string][]string{}
+	x86_64LinkFlags            = []string{}
+
+	x86_64ArchVariantRustFlags = map[string][]string{
+		"":            []string{},
+		"broadwell":   []string{"-C target-cpu=broadwell"},
+		"haswell":     []string{"-C target-cpu=haswell"},
+		"ivybridge":   []string{"-C target-cpu=ivybridge"},
+		"sandybridge": []string{"-C target-cpu=sandybridge"},
+		"silvermont":  []string{"-C target-cpu=silvermont"},
+		"skylake":     []string{"-C target-cpu=skylake"},
+		//TODO: Add target-cpu=stoneyridge when rustc supports it.
+		"stoneyridge": []string{""},
+	}
+)
+
+func init() {
+	registerToolchainFactory(android.Android, android.X86_64, x86_64ToolchainFactory)
+
+	pctx.StaticVariable("x86_64ToolchainRustFlags", strings.Join(x86_64RustFlags, " "))
+	pctx.StaticVariable("x86_64ToolchainLinkFlags", strings.Join(x86_64LinkFlags, " "))
+
+	for variant, rustFlags := range x86_64ArchVariantRustFlags {
+		pctx.StaticVariable("X86_64"+variant+"VariantRustFlags",
+			strings.Join(rustFlags, " "))
+	}
+
+}
+
+type toolchainX86_64 struct {
+	toolchain64Bit
+	toolchainRustFlags string
+}
+
+func (t *toolchainX86_64) RustTriple() string {
+	return "x86_64-unknown-linux-gnu"
+}
+
+func (t *toolchainX86_64) ToolchainLinkFlags() string {
+	return "${config.x86_64ToolchainLinkFlags}"
+}
+
+func (t *toolchainX86_64) ToolchainRustFlags() string {
+	return t.toolchainRustFlags
+}
+
+func (t *toolchainX86_64) RustFlags() string {
+	return "${config.x86_64ToolchainRustFlags}"
+}
+
+func x86_64ToolchainFactory(arch android.Arch) Toolchain {
+	toolchainRustFlags := []string{
+		"${config.x86_64ToolchainRustFlags}",
+		"${config.X86_64" + arch.ArchVariant + "VariantRustFlags}",
+	}
+
+	for _, feature := range arch.ArchFeatures {
+		toolchainRustFlags = append(toolchainRustFlags, x86_64ArchFeatureRustFlags[feature]...)
+	}
+
+	return &toolchainX86_64{
+		toolchainRustFlags: strings.Join(toolchainRustFlags, " "),
+	}
+}