extend/ENV/super: avoid adding llvm to HOMEBREW_LIBRARY_PATHS

This leads to undesired linkage with LLVM's `libunwind` (because it
shadows the system's `libunwind`).

See, for example, Homebrew/homebrew-core#169354.

Library/Homebrew/extend/ENV/super.rb

@@ -229,7 +229,9 @@ module Superenv
       end
     end
 
-    paths << keg_only_deps.map(&:opt_lib)
+    # Don't add `llvm` to library paths; this leads to undesired linkage to LLVM's `libunwind`
+    paths << keg_only_deps.reject { |dep| dep.name.match?(/^llvm(@\d+)?$/) }
+                          .map(&:opt_lib)
     paths << (HOMEBREW_PREFIX/"lib")
 
     paths += homebrew_extra_library_paths