Use both getrandom() and /dev/urandom by default on Linux.
Use both getrandom() and /dev/urandom by default on Linux.

getrandom() is now used on Linux by default when using Linux >= 3.17
and glibc >= 2.25

Reviewed-by: Rich Salz <c04971a99e5a9ee80eaab4b1deb37e845b0bd697@openssl.org>
GH: #5314

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl