params: avoid using intmax_t since it's not well supported

params: avoid using intmax_t since it's not well supported

Converting doubles to integers used to go via intmax_t which isn't properly
defined on some platforms.  The alternative is to go via int64_t.

Fixes #15815
Alternative to #15816

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15817)