Clean up Config::libdir_relative

Author: Mark-Simulacrum

src/bootstrap/builder.rs

@@ -541,8 +541,8 @@ 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() {
-                    config.libdir_relative().unwrap()
+                let lib = if compiler.stage >= 1 {
+                    config.libdir_relative()
                 } else {
                     Path::new("lib")
                 };
@@ -736,7 +736,7 @@ impl<'a> Builder<'a> {
             .env("CFG_VERSION", self.rust_version())
             .env("CFG_PREFIX", &self.config.install.prefix);
 
-        let libdir_relative = self.config.libdir_relative().unwrap_or(Path::new("lib"));
+        let libdir_relative = self.config.libdir_relative();
         cargo.env("CFG_LIBDIR_RELATIVE", libdir_relative);
 
         // If we're not building a compiler with debugging information then remove

src/bootstrap/config.rs

@@ -572,13 +572,13 @@ impl Config {
     }
 
     /// Try to find the relative path of `libdir`.
-    pub fn libdir_relative(&self) -> Option<&Path> {
-        let libdir = self.install.libdir.as_ref()?;
+    pub fn libdir_relative(&self) -> &Path {
+        let libdir = &self.install.libdir;
         if libdir.is_relative() {
-            Some(libdir)
+            libdir
         } else {
             // Try to make it relative to the prefix.
-            libdir.strip_prefix(self.prefix.as_ref()?).ok()
+            libdir.strip_prefix(&self.install.prefix).unwrap_or(Path::new("lib"))
         }
     }