llvm/clang/test/Driver/darwin-warning-options.c

// Always error about undefined 'TARGET_OS_*' macros on Darwin.
// RUN: %clang -### --target=arm64-apple-darwin %s 2>&1 | FileCheck %s

// CHECK-DAG: "-Wundef-prefix=TARGET_OS_"
// CHECK-DAG: "-Werror=undef-prefix"