fips: add function to detect if the self tests are running

Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Viktor Dukhovni <viktor@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/26838)

include/internal/fips.h

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2025 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License 2.0 (the "License").  You may not use
+ * this file except in compliance with the License.  You can obtain a copy
+ * in the file LICENSE in the source distribution or at
+ * https://www.openssl.org/source/license.html
+ */
+
+#ifndef OSSL_INTERNAL_FIPS_H
+# define OSSL_INTERNAL_FIPS_H
+# pragma once
+
+# ifdef FIPS_MODULE
+
+/* Return 1 if the FIPS self tests are running and 0 otherwise */
+int ossl_fips_self_testing(void);
+
+# endif /* FIPS_MODULE */
+
+#endif