Add atexit configuration option to using atexit() in libcrypto at build-time.

Add atexit configuration option to using atexit() in libcrypto at build-time.

This fixes an issue with a mix of atexit() usage in DLL and statically linked
libcrypto that came out in the test suite on NonStop, which has slightly
different DLL unload processing semantics compared to Linux. The change
allows a build configuration to select whether to register OPENSSL_cleanup()
with atexit() or not, so avoid situations where atexit() registration causes
SIGSEGV.

INSTALL.md and CHANGES.md have been modified to include and describe this
option.

Signed-off-by: Randall S. Becker <randall.becker@nexbridge.ca>
Signed-off-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23642)

(cherry picked from commit 0e1989d4c7435809b60f614c23ba8c9a7c0373e8)