Auto merge of rust-lang#121395 - nikic:update-llvm-21, r=<try>

Update to LLVM 18.1.0 rc 3

Fixes rust-lang#120819.
Fixes rust-lang#121180.
Fixes rust-lang#121239.
Fixes rust-lang#121367.

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

@@ -2026,7 +2026,13 @@ fn install_llvm_file(builder: &Builder<'_>, source: &Path, destination: &Path) {
         return;
     }
 
-    builder.install(source, destination, 0o644);
+    if source.is_symlink() {
+        // Follow symlinks. E.g. if we're linking against libLLVM-18.so, then what gets loaded
+        // at runtime is libLLVM.so.18.1.
+        builder.install(&t!(fs::canonicalize(source)), destination, 0o644);
+    } else {
+        builder.install(&source, destination, 0o644);
+    }
 }
 
 /// Maybe add LLVM object files to the given destination lib-dir. Allows either static or dynamic linking.

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

@@ -98,9 +98,6 @@ pub fn prebuilt_llvm_config(
     let out_dir = builder.llvm_out(target);
 
     let mut llvm_config_ret_dir = builder.llvm_out(builder.config.build);
-    if (!builder.config.build.is_msvc() || builder.ninja()) && !builder.config.llvm_from_ci {
-        llvm_config_ret_dir.push("build");
-    }
     llvm_config_ret_dir.push("bin");
     let build_llvm_config = llvm_config_ret_dir.join(exe("llvm-config", builder.config.build));
     let llvm_cmake_dir = out_dir.join("lib/cmake/llvm");