CI: pin lld+llvm to version 19 on macOS

Author: Xmader

setup.sh

@@ -18,7 +18,7 @@ if [[ "$OSTYPE" == "linux-gnu"* ]]; then # Linux
 elif [[ "$OSTYPE" == "darwin"* ]]; then # macOS
   brew update || true # allow failure
   brew install cmake pkg-config wget unzip coreutils # `coreutils` installs the `realpath` command
-  brew install lld
+  brew install lld@19
 elif [[ "$OSTYPE" == "msys"* ]]; then # Windows
   echo "Dependencies are not going to be installed automatically on Windows."
 else