Rollup merge of #152609 - mati865:gnullvm-llvm-dll, r=bjorn3

Install LLVM DLL in the right place on Windows

Continuation of https://github.com/rust-lang/rust/pull/151795 towards https://github.com/rust-lang/rust/issues/151774.

Unlike other systems, Windows requires runtime libraries to be present in `PATH` or right next to the binary.
So, we copy the library next to the binary as the easier solution.

Tested building `rust-openssl` in debug and release modes, but the difference is within noise margin.

compiler/rustc_metadata/src/native_libs.rs

@@ -61,6 +61,8 @@ pub fn walk_native_lib_search_dirs<R>(
     // library directory instead of the self-contained directories.
     // Sanitizer libraries have the same issue and are also linked by name on Apple targets.
     // The targets here should be in sync with `copy_third_party_objects` in bootstrap.
+    // Finally there is shared LLVM library, which unlike compiler libraries, is linked by the name,
+    // therefore requiring the search path for the linker.
     // FIXME: implement `-Clink-self-contained=+/-unwind,+/-sanitizers`, move the shipped libunwind
     // and sanitizers to self-contained directory, and stop adding this search path.
     // FIXME: On AIX this also has the side-effect of making the list of library search paths
@@ -71,6 +73,9 @@ pub fn walk_native_lib_search_dirs<R>(
         || sess.target.os == Os::Fuchsia
         || sess.target.is_like_aix
         || sess.target.is_like_darwin && !sess.sanitizers().is_empty()
+        || sess.target.os == Os::Windows
+            && sess.target.env == Env::Gnu
+            && sess.target.abi == Abi::Llvm
     {
         f(&sess.target_tlib_path.dir, false)?;
     }