Rollup merge of #164134 - danieljhkim:fix-rust-objcopy-rpath, r=Kobzol

bootstrap: add an rpath to LLVM library for LLVM tools

Closes [#164063](#164063) by adding rpath to the LLVM tool executables on both Linux and macOS, using the same approach as Lld::run.

This PR is now written by a human, resubmitting [#164064](#164064) which was diagnosed and written by Claude.

**Validation:**

macOS
```bash
❯ otool -l ~/workspace/repos/rust/build/aarch64-apple-darwin/llvm/bin/llvm-objcopy | grep -A2 LC_RPATH
          cmd LC_RPATH
      cmdsize 40
         path @loader_path/../../../ (offset 12)
--
          cmd LC_RPATH
      cmdsize 32
         path @loader_path/../lib (offset 12)

❯ otool -L build/aarch64-apple-darwin/llvm/lib/libLLVM.dylib
build/aarch64-apple-darwin/llvm/lib/libLLVM.dylib:
        @rpath/libLLVM.dylib (compatibility version 1.0.0, current version 23.1.3)
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1359.0.0)
        /usr/lib/libz.1.dylib (compatibility version 1.0.0, current version 1.2.12)
        /usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 2200.27.0)
```

linux
```bash
readelf -d build/x86_64-unknown-linux-gnu/llvm/bin/llvm-objcopy | grep RUNPATH
 0x000000000000001d (RUNPATH)            Library runpath: [$ORIGIN/../../../:$ORIGIN/../lib:$ORIGIN/../lib/x86_64-unknown-linux-gnu]
```

Author: jhpratt

src/bootstrap/download-ci-llvm-stamp

@@ -1,4 +1,4 @@
 Change this file to make users of the `download-ci-llvm` configuration download
 a new version of LLVM from CI, even if the LLVM submodule hasn’t changed.
 
-Last change is for: https://github.com/rust-lang/rust/pull/163954
+Last change is for: https://github.com/rust-lang/rust/pull/164134

src/bootstrap/src/core/build_steps/llvm.rs

@@ -566,6 +566,16 @@ impl CommandLineStep for Llvm {
         // Keep the pre-LLVM23 behavior for now.
         cfg.define("LLVM_VERSIONED_DYLIB_NAME_ON_DARWIN", "OFF");
 
+        if link_shared {
+            // We inform LLVM tools where they can find the LLVM library
+            // by adding an rpath entry to the expected parent `lib` directory,
+            // e.g. `rust-objcopy` is shipped in `lib/rustlib/<host>/bin`.
+            if let Some(rpath) = llvm_lib_rpath(builder, target) {
+                ldflags.exe.push(" ");
+                ldflags.exe.push(rpath);
+            }
+        }
+
         if (target.starts_with("csky")
             || target.starts_with("riscv")
             || target.starts_with("sparc-"))
@@ -1162,6 +1172,23 @@ fn get_var(var_base: &str, host: &str, target: &str) -> Option<OsString> {
         .or_else(|| env::var_os(var_base))
 }
 
+/// Generate a RPATH entry for a binary that will link to LLVM (libLLVM.so) dynamically.
+/// This will make it possible to execute the binary outside Rustup, so that it can still find the libLLVM.so file.
+fn llvm_lib_rpath(builder: &Builder<'_>, target: TargetSelection) -> Option<&'static str> {
+    if builder.config.rpath_enabled(target) && helpers::use_host_linker(target) {
+        // Be careful when changing this path, we need to ensure it's quoted or escaped:
+        // `$ORIGIN` would otherwise be expanded when the `LdFlags` are passed verbatim to
+        // cmake.
+        if target.contains("linux") {
+            return Some("-Wl,-rpath,'$ORIGIN/../../../'");
+        }
+        if target.contains("apple-darwin") {
+            return Some("-Wl,-rpath,'@loader_path/../../../'");
+        }
+    }
+    None
+}
+
 #[derive(Clone)]
 pub struct BuiltRustOffload {
     /// Path to the rust offload dylib
@@ -1436,19 +1463,12 @@ impl CommandLineStep for OmpOffload {
             ldflags.push_all(format!("-L{}", dir.display()));
         }
 
-        if builder.config.rpath_enabled(target)
-            && helpers::use_host_linker(target)
-            && llvm_output.link_shared()
-            && target.contains("linux")
-        {
-            // Same logic as in Lld::run
+        if llvm_output.link_shared() {
             // We inform libomptarget.so where it can find LLVM's libraries
             // by adding an rpath entry to the expected parent `lib` directory.
-            //
-            // Be careful when changing this path, we need to ensure it's quoted or escaped:
-            // `$ORIGIN` would otherwise be expanded when the `LdFlags` are passed verbatim to
-            // cmake.
-            ldflags.push_all("-Wl,-rpath,'$ORIGIN/../../../'");
+            if let Some(rpath) = llvm_lib_rpath(builder, target) {
+                ldflags.push_all(rpath);
+            }
         }
 
         configure_cmake(builder, target, &mut cfg, true, ldflags, cflags, &[]);
@@ -1724,21 +1744,11 @@ impl CommandLineStep for Lld {
         // component installed, one can successfully invoke `rust-lld` directly without rustup's
         // `LD_LIBRARY_PATH` overrides)
         //
-        if builder.config.rpath_enabled(target)
-            && helpers::use_host_linker(target)
-            && llvm_output.link_shared()
-        {
+        if llvm_output.link_shared() {
             // So we inform LLD where it can find LLVM's libraries by adding an rpath entry to the
             // expected parent `lib` directory.
-            //
-            // Be careful when changing this path, we need to ensure it's quoted or escaped:
-            // `$ORIGIN` would otherwise be expanded when the `LdFlags` are passed verbatim to
-            // cmake.
-            if target.contains("linux") {
-                ldflags.push_all("-Wl,-rpath,'$ORIGIN/../../../'");
-            }
-            if target.contains("apple-darwin") {
-                ldflags.push_all("-Wl,-rpath,'@loader_path/../../../'");
+            if let Some(rpath) = llvm_lib_rpath(builder, target) {
+                ldflags.push_all(rpath);
             }
         }