Add linux_musl arm+arm64

Add toolchains to support cross compiling to aarch64-linux-musl and
arm-linux-musleabihf.

Bug: 236052820
Test: build arm and arm64 musl sysroots
Change-Id: I47a9322929baff2492c6e8db989ece01fcbeb133
diff --git a/android/arch.go b/android/arch.go
index cbf77c7..382a7df 100644
--- a/android/arch.go
+++ b/android/arch.go
@@ -307,7 +307,7 @@
 	// Linux is the OS for the Linux kernel plus the glibc runtime.
 	Linux = newOsType("linux_glibc", Host, false, X86, X86_64)
 	// LinuxMusl is the OS for the Linux kernel plus the musl runtime.
-	LinuxMusl = newOsType("linux_musl", Host, false, X86, X86_64)
+	LinuxMusl = newOsType("linux_musl", Host, false, X86, X86_64, Arm64, Arm)
 	// Darwin is the OS for MacOS/Darwin host machines.
 	Darwin = newOsType("darwin", Host, false, Arm64, X86_64)
 	// LinuxBionic is the OS for the Linux kernel plus the Bionic libc runtime, but without the