message: tconfig MFEM_USE_SIMD definitions fix
diff: #ifndef MFEM_USE_SIMD
  #include "simd/auto.hpp"
  #else
  -#ifdef __VSX__
  +#if defined(__VSX__)
  #include "simd/vsx128.hpp"
  -#endif
  -#ifdef __bgq__
  +#elif defined (__bgq__)
  #include "simd/qpx.hpp"
  -#else
  +#elif defined(__x86_64__)
  #include "simd/x86.hpp"
  +#else
  +#error Unknown SIMD architecture
  #endif
  #endif
  