The former is deprecated by C++14. The standard says they are the same:

The header defines all types and macros the same as the C standard library
header<stdint.h>.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

The former is deprecated with C++14. The standard says both are the same:

The contents and meaning of the header<cstddef>are the same as the C
standard library header<stddef.h>,except that it does not declare the type
wchar_t, that it also declares the type byte and its associated
operations (21.2.5), and as noted in 21.2.3 and 21.2.4.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Prepare for using other crypto libraries, e.g. FFmpeg's libavutil.