Instead of using the internal DRBG-based RNG, use the `getrandom()` system
call where available.
Keep the existing version as fall-back for other systems that don't provide
that system call.
... and for cases where auto-detection fails or the user simply wants to
use the internal RNG a new configure-switch is provided.
Signed-off-by: Steffen Jaeckel <jaeckel-floss@eyet-services.de>
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