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
diff --git a/android/arch.go b/android/arch.go
index 9bc9d89..75ee922 100644
--- a/android/arch.go
+++ b/android/arch.go
@@ -147,10 +147,11 @@
 var (
 	archTypeList []ArchType
 
-	Arm    = newArch("arm", "lib32")
-	Arm64  = newArch("arm64", "lib64")
-	X86    = newArch("x86", "lib32")
-	X86_64 = newArch("x86_64", "lib64")
+	Arm     = newArch("arm", "lib32")
+	Arm64   = newArch("arm64", "lib64")
+	Riscv64 = newArch("riscv64", "lib64")
+	X86     = newArch("x86", "lib32")
+	X86_64  = newArch("x86_64", "lib64")
 
 	Common = ArchType{
 		Name: COMMON_VARIANT,
@@ -318,7 +319,7 @@
 	Windows = newOsType("windows", Host, true, X86, X86_64)
 	// Android is the OS for target devices that run all of Android, including the Linux kernel
 	// and the Bionic libc runtime.
-	Android = newOsType("android", Device, false, Arm, Arm64, X86, X86_64)
+	Android = newOsType("android", Device, false, Arm, Arm64, Riscv64, X86, X86_64)
 
 	// CommonOS is a pseudo OSType for a common OS variant, which is OsType agnostic and which
 	// has dependencies on all the OS variants.
diff --git a/android/arch_test.go b/android/arch_test.go
index 6814f8a..46c018a 100644
--- a/android/arch_test.go
+++ b/android/arch_test.go
@@ -596,6 +596,7 @@
 				arm64: {
 					a:  ["arm64"],
 				},
+				riscv64: { a: ["riscv64"] },
 				x86: { a:  ["x86"] },
 				x86_64: { a:  ["x86_64"] },
 			},