propagate --target only if target is not host

Passing `--target` alters `RUSTFLAGS` in the build scripts. Since there is no reason
to pass them when building for the host triple, exclude them if the target is the host triple.

Signed-off-by: onur-ozkan <work@onurozkan.dev>

src/bootstrap/src/core/builder.rs

@@ -1343,10 +1343,9 @@ impl<'a> Builder<'a> {
             Color::Auto => {} // nothing to do
         }
 
-        if cmd != "install" {
+        if target != compiler.host {
+            assert!(cmd != "install", "`x install` can only be called for the host triple.");
             cargo.arg("--target").arg(target.rustc_target_arg());
-        } else {
-            assert_eq!(target, compiler.host);
         }
 
         if self.config.rust_optimize.is_release() {

src/bootstrap/src/lib.rs

@@ -797,7 +797,13 @@ impl Build {
     /// running a particular compiler, whether or not we're building the
     /// standard library, and targeting the specified architecture.
     fn cargo_out(&self, compiler: Compiler, mode: Mode, target: TargetSelection) -> PathBuf {
-        self.stage_out(compiler, mode).join(&*target.triple).join(self.cargo_dir())
+        let stage_out = self.stage_out(compiler, mode);
+
+        if self.config.build == target {
+            stage_out.join(self.cargo_dir())
+        } else {
+            stage_out.join(&*target.triple).join(self.cargo_dir())
+        }
     }
 
     /// Root output directory of LLVM for `target`