e_os.h: omit PRIu64.

PRIu64 is error-prone with BIO_printf, so introduce and stick to custom
platform-neutral macro. 'll' allows to print 64-bit values on *all*
supported platforms, but it's problematic with -Wformat -Werror. Hence
use 'l' in identifiable LP64 cases.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3148)