Rename sysroot directories to be more clear

src/bootstrap/bootstrap.py

@@ -597,7 +597,7 @@ def bin_root(self):
         >>> rb.bin_root() == os.path.join("build", "devel", "stage0")
         True
         """
-        subdir = "stage0"
+        subdir = "bootstrap-sysroot"
         return os.path.join(self.build_dir, self.build, subdir)
 
     def get_toml(self, key, section=None):

src/bootstrap/compile.rs

@@ -1106,9 +1106,7 @@ impl Step for Sysroot {
         let compiler = self.compiler;
         let host_dir = builder.out.join(&compiler.host.triple);
         let sysroot = if compiler.stage == 0 {
-            host_dir.join("stage0-sysroot")
-        } else if builder.download_rustc() {
-            host_dir.join("ci-rustc-sysroot")
+            host_dir.join("bootstrap-sysroot")
         } else {
             host_dir.join(format!("stage{}", compiler.stage))
         };