Rename rustc_back::target to rustc_target::spec.

Author: irinagpopa

src/Cargo.lock

@@ -18,7 +18,7 @@ lazy_static = "1.0.0"
 log = { version = "0.4", features = ["release_max_level_info", "std"] }
 proc_macro = { path = "../libproc_macro" }
 rustc_apfloat = { path = "../librustc_apfloat" }
-rustc_back = { path = "../librustc_back" }
+rustc_target = { path = "../librustc_target" }
 rustc_const_math = { path = "../librustc_const_math" }
 rustc_data_structures = { path = "../librustc_data_structures" }
 rustc_errors = { path = "../librustc_errors" }