constexpr_directive

// now using auto configuration via bit_cast.hpp which will define
// BIT_CAST_IS_CONSTEXPR == true if bit_cast is supported

#if defined(__clang__)
/* Clang/LLVM. ---------------------------------------------- */

#elif defined(__ICC) || defined(__INTEL_COMPILER)
/* Intel ICC/ICPC. ------------------------------------------ */


#elif defined(__GNUC__) || defined(__GNUG__)
/* GNU GCC/G++. --------------------------------------------- */

#elif defined(__HP_cc) || defined(__HP_aCC)
/* Hewlett-Packard C/aC++. ---------------------------------- */

#elif defined(__IBMC__) || defined(__IBMCPP__)
/* IBM XL C/C++. -------------------------------------------- */

#elif defined(_MSC_VER)
/* Microsoft Visual Studio. --------------------------------- */

#elif defined(__PGI)
/* Portland Group PGCC/PGCPP. ------------------------------- */

#elif defined(__SUNPRO_C) || defined(__SUNPRO_CC)
/* Oracle Solaris Studio. ----------------------------------- */

#endif