Replace libLLVM symlink with linker script

It turns out that the libLLVM-N.so -> libLLVM.so.N.1 symlink is
also needed when projects like miri link against librustc_driver.so.
As such, we have to distribute it in real rustup components like
rustc-dev, rather than only for download-ci-llvm.

To avoid actually distributing symlinks (which are not supported
or not fully supported by the rustup infrastructure) replace it
with a linker script that does the same thing instead.

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

@@ -2021,12 +2021,7 @@ fn add_env(builder: &Builder<'_>, cmd: &mut Command, target: TargetSelection) {
     }
 }
 
-fn install_llvm_file(
-    builder: &Builder<'_>,
-    source: &Path,
-    destination: &Path,
-    install_symlink: bool,
-) {
+fn install_llvm_file(builder: &Builder<'_>, source: &Path, destination: &Path) {
     if builder.config.dry_run() {
         return;
     }
@@ -2035,11 +2030,15 @@ fn install_llvm_file(
         // If we have a symlink like libLLVM-18.so -> libLLVM.so.18.1, install the target of the
         // symlink, which is what will actually get loaded at runtime.
         builder.install(&t!(fs::canonicalize(source)), destination, 0o644);
-        if install_symlink {
-            // If requested, also install the symlink. This is used by download-ci-llvm.
-            let full_dest = destination.join(source.file_name().unwrap());
-            builder.copy(&source, &full_dest);
-        }
+
+        // Replace the symlink itself with an equivalent linker script. This is used by
+        // download-ci-llvm and projects linking against librustc_driver.so. We don't use a
+        // symlink, as these are not allowed inside rustup components.
+        let link = t!(fs::read_link(source));
+        t!(std::fs::write(
+            destination.join(source.file_name().unwrap()),
+            format!("INPUT({})", link.display())
+        ));
     } else {
         builder.install(&source, destination, 0o644);
     }
@@ -2048,12 +2047,7 @@ fn install_llvm_file(
 /// Maybe add LLVM object files to the given destination lib-dir. Allows either static or dynamic linking.
 ///
 /// Returns whether the files were actually copied.
-fn maybe_install_llvm(
-    builder: &Builder<'_>,
-    target: TargetSelection,
-    dst_libdir: &Path,
-    install_symlink: bool,
-) -> bool {
+fn maybe_install_llvm(builder: &Builder<'_>, target: TargetSelection, dst_libdir: &Path) -> bool {
     // If the LLVM was externally provided, then we don't currently copy
     // artifacts into the sysroot. This is not necessarily the right
     // choice (in particular, it will require the LLVM dylib to be in
@@ -2102,7 +2096,7 @@ fn maybe_install_llvm(
             } else {
                 PathBuf::from(file)
             };
-            install_llvm_file(builder, &file, dst_libdir, install_symlink);
+            install_llvm_file(builder, &file, dst_libdir);
         }
         !builder.config.dry_run()
     } else {
@@ -2117,7 +2111,7 @@ pub fn maybe_install_llvm_target(builder: &Builder<'_>, target: TargetSelection,
     // dynamically linked; it is already included into librustc_llvm
     // statically.
     if builder.llvm_link_shared() {
-        maybe_install_llvm(builder, target, &dst_libdir, false);
+        maybe_install_llvm(builder, target, &dst_libdir);
     }
 }
 
@@ -2129,7 +2123,7 @@ pub fn maybe_install_llvm_runtime(builder: &Builder<'_>, target: TargetSelection
     // dynamically linked; it is already included into librustc_llvm
     // statically.
     if builder.llvm_link_shared() {
-        maybe_install_llvm(builder, target, &dst_libdir, false);
+        maybe_install_llvm(builder, target, &dst_libdir);
     }
 }
 
@@ -2224,8 +2218,6 @@ impl Step for RustDev {
 
         let mut tarball = Tarball::new(builder, "rust-dev", &target.triple);
         tarball.set_overlay(OverlayKind::LLVM);
-        // LLVM requires a shared object symlink to exist on some platforms.
-        tarball.permit_symlinks(true);
 
         builder.ensure(crate::core::build_steps::llvm::Llvm { target });
 
@@ -2266,7 +2258,7 @@ impl Step for RustDev {
         // of `rustc-dev` to support the inherited `-lLLVM` when using the
         // compiler libraries.
         let dst_libdir = tarball.image_dir().join("lib");
-        maybe_install_llvm(builder, target, &dst_libdir, true);
+        maybe_install_llvm(builder, target, &dst_libdir);
         let link_type = if builder.llvm_link_shared() { "dynamic" } else { "static" };
         t!(std::fs::write(tarball.image_dir().join("link-type.txt"), link_type), dst_libdir);