Workaround crash in atexit on NonStop platforms

Workaround crash in atexit on NonStop platforms

We cannot dynamically load the legacy provider into an application
that is linked statically to libcrypto as this causes
a double loading of libcrypto (one static and one dynamic) and
on NonStop this leads to a segfault in atexit().

Fixes #17537

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19844)