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

bazel/configurability.go

@@ -23,10 +23,11 @@ import (
 
 const (
 	// ArchType names in arch.go
-	archArm    = "arm"
-	archArm64  = "arm64"
-	archX86    = "x86"
-	archX86_64 = "x86_64"
+	archArm     = "arm"
+	archArm64   = "arm64"
+	archRiscv64 = "riscv64"
+	archX86     = "x86"
+	archX86_64  = "x86_64"
 
 	// OsType names in arch.go
 	OsAndroid     = "android"
@@ -39,6 +40,7 @@ const (
 	// Targets in arch.go
 	osArchAndroidArm        = "android_arm"
 	osArchAndroidArm64      = "android_arm64"
+	osArchAndroidRiscv64    = "android_riscv64"
 	osArchAndroidX86        = "android_x86"
 	osArchAndroidX86_64     = "android_x86_64"
 	osArchDarwinArm64       = "darwin_arm64"
@@ -99,6 +101,7 @@ func createPlatformArchMap() map[string]string {
 		"arm64": {
 			"dotprod",
 		},
+		"riscv64": {},
 		"x86": {
 			"ssse3",
 			"sse4",
@@ -164,6 +167,7 @@ var (
 	platformOsArchMap = map[string]string{
 		osArchAndroidArm:           "//build/bazel/platforms/os_arch:android_arm",
 		osArchAndroidArm64:         "//build/bazel/platforms/os_arch:android_arm64",
+		osArchAndroidRiscv64:       "//build/bazel/platforms/os_arch:android_riscv64",
 		osArchAndroidX86:           "//build/bazel/platforms/os_arch:android_x86",
 		osArchAndroidX86_64:        "//build/bazel/platforms/os_arch:android_x86_64",
 		osArchDarwinArm64:          "//build/bazel/platforms/os_arch:darwin_arm64",
@@ -187,7 +191,7 @@ var (
 	// TODO(cparsons): Source from arch.go; this task is nontrivial, as it currently results
 	// in a cyclic dependency.
 	osToArchMap = map[string][]string{
-		OsAndroid:     {archArm, archArm64, archX86, archX86_64},
+		OsAndroid:     {archArm, archArm64, archRiscv64, archX86, archX86_64},
 		osLinux:       {archX86, archX86_64},
 		osLinuxMusl:   {archX86, archX86_64},
 		osDarwin:      {archArm64, archX86_64},