don't use entire sysroot binary path for rustc tarballs

Previously, we used the entire sysroot binary path to prepare rustc tarballs.
Since we also copy tool binaries to the sysroot binary path, installing rustc
and tools with `x install` results in attempting to install the same binaries
more than once. This causes rust-installer to create backup files (*.old) due
to file conflicts. This change fixes that.

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

Author: onur-ozkan

src/bootstrap/src/core/build_steps/dist.rs

@@ -398,10 +398,11 @@ impl Step for Rustc {
             let host = compiler.host;
             let src = builder.sysroot(compiler);
 
-            // Copy rustc/rustdoc binaries
+            // Copy rustc binary
+            builder.install(&src.join("bin").join(exe("rustc", host)), &image.join("bin"), 0o755);
             t!(fs::create_dir_all(image.join("bin")));
-            builder.cp_r(&src.join("bin"), &image.join("bin"));
 
+            // If enabled, copy rustdoc binary
             if builder
                 .config
                 .tools