[release/8.0] Remove Homebrew LLVM during macOS CI setup - Part 2 (#125790)

The CI runner image may ship with a Homebrew LLVM whose libraries (e.g.,
an x86_64-only libunwind.dylib in /usr/local/lib) conflict with the
Apple SDK and break native linking. The build uses Apple clang from
/usr/bin/clang exclusively and does not need Homebrew LLVM.

Backport of #125763

Co-authored-by: vseanreesermsft <78103370+vseanreesermsft@users.noreply.github.com>

Author: steveisok

eng/install-native-dependencies.sh

@@ -45,7 +45,7 @@ case "$os" in
         # Homebrew LLVM whose libraries (e.g., libunwind.dylib) are the wrong
         # architecture or conflict with the Apple SDK, breaking native linking.
         # The build uses Apple clang from /usr/bin/clang exclusively.
-        brew uninstall --ignore-dependencies llvm 2>/dev/null || true
+        brew uninstall --ignore-dependencies llvm@18 2>/dev/null || true
 
         brew bundle --no-upgrade --file "$(dirname "$0")/Brewfile"
         ;;