Define OPENSSL_NO_SHA including OpenSSL from test.

We don't use SHA256 from OpenSSL in the sk-dummy module and the
definitions can conflict with system sha2.h (eg on NetBSD) so define
OPENSSL_NO_SHA so we don't attempt to redefine them.

regress/misc/sk-dummy/sk-dummy.c

@@ -36,6 +36,8 @@
 #endif
 
 #ifdef WITH_OPENSSL
+/* We don't use sha2 from OpenSSL and they can conflict with system sha2.h */
+#define OPENSSL_NO_SHA
 #include <openssl/opensslv.h>
 #include <openssl/crypto.h>
 #include <openssl/evp.h>