Configure: Check if 128-bit integers are supported by compiler
Add a config variable "use_int128" to indicate if 128-bit integers are
supported or not at the configure time. This makes it easier to
automatically select 64-bit versus 32-bit implementation for curve448.
Signed-off-by: Amitay Isaacs <amitay@ozlabs.org> Reviewed-by: Tomas Mraz <tomas@openssl.org> Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14784)