message: VSX tconfig logic
diff: #endif
  #endif
  -// --- Default SIMD and BLOCK sizes
  -#ifdef _WIN32
  -#define MFEM_SIMD_DEFAULT_SIZE 8
  -#define MFEM_TEMPLATE_BLOCK_DEFAULT_SIZE 1
  -#else
  -#define MFEM_SIMD_DEFAULT_SIZE 32
  -#define MFEM_TEMPLATE_BLOCK_DEFAULT_SIZE 4
  -#endif
  -
  // --- SIMD and BLOCK sizes
  -#ifndef MFEM_USE_SIMD
  -#define MFEM_SIMD_SIZE MFEM_SIMD_DEFAULT_SIZE
  -#define MFEM_TEMPLATE_BLOCK_SIZE MFEM_TEMPLATE_BLOCK_DEFAULT_SIZE
  -#else
  -#ifdef __VSX__
  +#if defined(_WIN32)
  +#define MFEM_SIMD_SIZE 8
  +#define MFEM_TEMPLATE_BLOCK_SIZE 1
  +#elif defined(__VSX__)
  #define MFEM_SIMD_SIZE 16
  #define MFEM_TEMPLATE_BLOCK_SIZE 2
  +#elif defined(__x86_64__)
  +#define MFEM_SIMD_SIZE 32
  +#define MFEM_TEMPLATE_BLOCK_SIZE 4
  #else
  -#define MFEM_SIMD_SIZE MFEM_SIMD_DEFAULT_SIZE
  -#define MFEM_TEMPLATE_BLOCK_SIZE MFEM_TEMPLATE_BLOCK_DEFAULT_SIZE
  -#endif
  +#error Unknown SIMD architecture
  #endif
  template<typename complex_t, typename real_t, bool simd>
  