aarch64-prep: Wrap x86_64 specific crate references with conditionals

Cargo.toml

@@ -79,7 +79,6 @@ path = "src/bin/watch.rs"
 extra = { git = "https://gitlab.redox-os.org/redox-os/libextra.git" }
 libflate = "0.1.4"
 pager = { git = "https://gitlab.redox-os.org/redox-os/libpager.git" }
-raw-cpuid = "2.0"
 redox_syscall = "0.1"
 tar = { git = "https://github.com/alexcrichton/tar-rs.git" }
 filetime = "0.1.10"
@@ -89,6 +88,8 @@ tree_magic = "0.2"
 bzip2 = "0.3"
 zip = "0.3"
 
+[target.'cfg(target_arch = "x86_64")'.dependencies]
+raw-cpuid = "2.0"
 
 [patch.crates-io]
 "filetime" = { git = "https://github.com/alexcrichton/filetime.git" }