message: tests: Fix expansion-to-defined warning
  This warning is new as of GCC 7 and highlights undefined behavior in the
  preprocessor that ASAN detection was relying on.
diff: #if defined(__has_feature)
  # define ADDRESS_SANITIZER __has_feature(address_sanitizer)
  #else
  -# define ADDRESS_SANITIZER defined(__SANITIZE_ADDRESS__)
  +# if defined(__SANITIZE_ADDRESS__)
  +# define ADDRESS_SANITIZER 1
  +# else
  +# define ADDRESS_SANITIZER 0
  +# endif
  #endif
  // Low-level allocation functions
  