rustc_target: Rename some target options to avoid tautology

`target.target_endian` -> `target.endian`
`target.target_c_int_width` -> `target.c_int_width`
`target.target_os` -> `target.os`
`target.target_env` -> `target.env`
`target.target_vendor` -> `target.vendor`
`target.target_family` -> `target.os_family`
`target.target_mcount` -> `target.mcount`

compiler/rustc_target/src/spec/linux_kernel_base.rs

@@ -8,7 +8,7 @@ pub fn opts() -> TargetOptions {
     );
 
     TargetOptions {
-        target_env: "gnu".to_string(),
+        env: "gnu".to_string(),
         disable_redzone: true,
         panic_strategy: PanicStrategy::Abort,
         stack_probes: true,