Fix double resolving custom libdir

src/bootstrap/builder.rs

@@ -627,13 +627,7 @@ impl<'a> Builder<'a> {
             }
 
             fn run(self, builder: &Builder<'_>) -> Interned<PathBuf> {
-                let compiler = self.compiler;
-                let config = &builder.build.config;
-                let lib = if compiler.stage >= 1 && config.libdir_relative().is_some() {
-                    builder.build.config.libdir_relative().unwrap()
-                } else {
-                    Path::new("lib")
-                };
+                let lib = builder.sysroot_libdir_relative(self.compiler);
                 let sysroot = builder
                     .sysroot(self.compiler)
                     .join(lib)
@@ -687,6 +681,18 @@ impl<'a> Builder<'a> {
         }
     }
 
+    /// Returns the compiler's relative libdir where the standard library and other artifacts are
+    /// found for a compiler's sysroot.
+    ///
+    /// For example this returns `lib` on Unix and Windows.
+    pub fn sysroot_libdir_relative(&self, compiler: Compiler) -> &Path {
+        match self.config.libdir_relative() {
+            Some(relative_libdir) if compiler.stage >= 1
+                => relative_libdir,
+            _ => Path::new("lib")
+        }
+    }
+
     /// Adds the compiler's directory of dynamic libraries to `cmd`'s dynamic
     /// library lookup path.
     pub fn add_rustc_lib_path(&self, compiler: Compiler, cmd: &mut Command) {

src/bootstrap/dist.rs

@@ -469,7 +469,6 @@ impl Step for Rustc {
         fn prepare_image(builder: &Builder<'_>, compiler: Compiler, image: &Path) {
             let host = compiler.host;
             let src = builder.sysroot(compiler);
-            let libdir = builder.rustc_libdir(compiler);
 
             // Copy rustc/rustdoc binaries
             t!(fs::create_dir_all(image.join("bin")));
@@ -481,20 +480,26 @@ impl Step for Rustc {
 
             // Copy runtime DLLs needed by the compiler
             if libdir_relative.to_str() != Some("bin") {
+                let libdir = builder.rustc_libdir(compiler);
                 for entry in builder.read_dir(&libdir) {
                     let name = entry.file_name();
                     if let Some(s) = name.to_str() {
                         if is_dylib(s) {
-                            builder.install(&entry.path(), &image.join(&libdir_relative), 0o644);
+                            // Don't use custom libdir here because ^lib/ will be resolved again
+                            // with installer
+                            builder.install(&entry.path(), &image.join("lib"), 0o644);
                         }
                     }
                 }
             }
 
             // Copy over the codegen backends
             let backends_src = builder.sysroot_codegen_backends(compiler);
-            let backends_rel = backends_src.strip_prefix(&src).unwrap();
-            let backends_dst = image.join(&backends_rel);
+            let backends_rel = backends_src.strip_prefix(&src).unwrap()
+                .strip_prefix(builder.sysroot_libdir_relative(compiler)).unwrap();
+            // Don't use custom libdir here because ^lib/ will be resolved again with installer
+            let backends_dst = image.join("lib").join(&backends_rel);
+
             t!(fs::create_dir_all(&backends_dst));
             builder.cp_r(&backends_src, &backends_dst);