Fix libgccjit symlink when we build GCC locally

Author: Kobzol

src/bootstrap/src/core/build_steps/gcc.rs

@@ -39,8 +39,16 @@ impl GccOutput {
         let mut target_filename = self.libgccjit.file_name().unwrap().to_str().unwrap().to_string();
         target_filename.push_str(".0");
 
+        // If we build libgccjit ourselves, then `self.libgccjit` can actually be a symlink.
+        // In that case, we have to resolve it first, otherwise we'd create a symlink to a symlink,
+        // which wouldn't work.
+        let actual_libgccjit_path = t!(
+            self.libgccjit.canonicalize(),
+            format!("Cannot find libgccjit at {}", self.libgccjit.display())
+        );
+
         let dst = directory.join(target_filename);
-        builder.copy_link(&self.libgccjit, &dst, FileType::NativeLibrary);
+        builder.copy_link(&actual_libgccjit_path, &dst, FileType::NativeLibrary);
     }
 }