Tests/CMakeCommands/target_compile_definitions/consumer.c

#ifdef TEST_LANG_DEFINES
  #ifdef CONSUMER_LANG_CXX
  #error Unexpected CONSUMER_LANG_CXX
  #endif

  #ifndef CONSUMER_LANG_C
  #error Expected CONSUMER_LANG_C
  #endif

  #if !LANG_IS_C
  #error Expected LANG_IS_C
  #endif

  #if LANG_IS_CXX
  #error Unexpected LANG_IS_CXX
  #endif
#endif

void consumer_c()
{

}