Copy sha256-x86.c from https://github.com/noloader/SHA-Intrinsics, that
uses the compiler intrinsics to implement the update step with the
native x86_64 instructions.
To avoid dependencies of the reference code and the x86 version, check
runtime support only if the compiler also supports -msha.
Signed-off-by: David Sterba <dsterba@suse.com>
David Sterba