Merge pull request #435 from raphlinus/aarch64

Enable musl with aarch64
diff --git a/src/unix/notbsd/linux/musl/mod.rs b/src/unix/notbsd/linux/musl/mod.rs
index 69a85b8..1808e44 100644
--- a/src/unix/notbsd/linux/musl/mod.rs
+++ b/src/unix/notbsd/linux/musl/mod.rs
@@ -231,7 +231,7 @@
 }
 
 cfg_if! {
-    if #[cfg(any(target_arch = "x86_64"))] {
+    if #[cfg(any(target_arch = "x86_64", target_arch = "aarch64"))] {
         mod b64;
         pub use self::b64::*;
     } else if #[cfg(any(target_arch = "x86",