message: Fix compile errors when the '-mf16c' CFLAG is enabled.
  Fixes an issue where 'half.hpp' skips the 'immintrin.h' include
  statement if '-mf16c' is used.
  (which can happen when using '-march=native')
diff: #if HALF_ENABLE_CPP11_HASH
  #include <functional>
  #endif
  -#if HALF_ENABLE_F16C_INTRINSICS
  - #include <immintrin.h>
  -#endif
  #ifndef HALF_ENABLE_F16C_INTRINSICS
  #define HALF_ENABLE_F16C_INTRINSICS __F16C__
  #endif
  +#if HALF_ENABLE_F16C_INTRINSICS
  + #include <immintrin.h>
  +#endif
  +
  #ifdef HALF_DOXYGEN_ONLY
  /// Type for internal floating-point computations.
  /// This can be predefined to a built-in floating-point type (`float`, `double` or `long double`) to override the internal
  