Fix a stack smash

It occurs when memory compares are made that are larger
than the on stack temporary buffers (either malloced or supplied).

Rework the test test so it doesn't use a macro with a branch.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3155)