Modify 50-nonstop.conf to enable c99 extensions for uintptr_t.

Modify 50-nonstop.conf to enable c99 extensions for uintptr_t.

This is done using the define __NSK_OPTIONAL_TYPES__ and is specific to the
NonStop platform builds.

Fixes: #22002
Signed-off-by: Randall S. Becker <randall.becker@nexbridge.ca>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22005)