Add riscv64-linux-android support

Add barebones riscv64-linux-android support.  This should be enough
to add riscv64-specific entries to Android.bp files, but can't
actually compile anything until there are riscv64 toolchains.

Test: arch_test.go
Change-Id: I0dcc7e797d9352dd38243be908a7f19004ff3db1

rust/config/riscv64_device.go

@@ -0,0 +1,91 @@
+// Copyright 2022 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 (
+	Riscv64RustFlags            = []string{}
+	Riscv64ArchFeatureRustFlags = map[string][]string{"": {}}
+	Riscv64LinkFlags            = []string{}
+
+	Riscv64ArchVariantRustFlags = map[string][]string{}
+)
+
+func init() {
+	registerToolchainFactory(android.Android, android.Riscv64, Riscv64ToolchainFactory)
+
+	pctx.StaticVariable("Riscv64ToolchainRustFlags", strings.Join(Riscv64RustFlags, " "))
+	pctx.StaticVariable("Riscv64ToolchainLinkFlags", strings.Join(Riscv64LinkFlags, " "))
+
+	for variant, rustFlags := range Riscv64ArchVariantRustFlags {
+		pctx.StaticVariable("Riscv64"+variant+"VariantRustFlags",
+			strings.Join(rustFlags, " "))
+	}
+
+}
+
+type toolchainRiscv64 struct {
+	toolchain64Bit
+	toolchainRustFlags string
+}
+
+func (t *toolchainRiscv64) RustTriple() string {
+	return "riscv64-linux-android"
+}
+
+func (t *toolchainRiscv64) ToolchainLinkFlags() string {
+	// Prepend the lld flags from cc_config so we stay in sync with cc
+	return "${config.DeviceGlobalLinkFlags} ${cc_config.Riscv64Lldflags} ${config.Riscv64ToolchainLinkFlags}"
+}
+
+func (t *toolchainRiscv64) ToolchainRustFlags() string {
+	return t.toolchainRustFlags
+}
+
+func (t *toolchainRiscv64) RustFlags() string {
+	return "${config.Riscv64ToolchainRustFlags}"
+}
+
+func (t *toolchainRiscv64) Supported() bool {
+	return true
+}
+
+func (toolchainRiscv64) LibclangRuntimeLibraryArch() string {
+	return "riscv64"
+}
+
+func Riscv64ToolchainFactory(arch android.Arch) Toolchain {
+	archVariant := arch.ArchVariant
+
+	toolchainRustFlags := []string{
+		"${config.Riscv64ToolchainRustFlags}",
+		"${config.Riscv64" + archVariant + "VariantRustFlags}",
+	}
+
+	toolchainRustFlags = append(toolchainRustFlags, deviceGlobalRustFlags...)
+
+	for _, feature := range arch.ArchFeatures {
+		toolchainRustFlags = append(toolchainRustFlags, Riscv64ArchFeatureRustFlags[feature]...)
+	}
+
+	return &toolchainRiscv64{
+		toolchainRustFlags: strings.Join(toolchainRustFlags, " "),
+	}
+}