app_malloc() terminates execution if the allocation fails. The tests implement
their own app_malloc() in an attempt to reduce the amount of code pulled in.
This version also needs to terminate on failed allocation. The alternative
would be adding failed allocation checks pervasively throughout the apps's
commands.
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15836)