Make mcontext_t align 16

Author: ifreund

src/unix/linux_like/linux/musl/b64/aarch64/align.rs

@@ -15,6 +15,7 @@ s! {
         pub uc_mcontext: mcontext_t,
     }
 
+    #[repr(align(16))]
     pub struct mcontext_t {
         __regs: [u64; 36 + 512],
     }