sign-file: fix build error in sign-file.c with libressl

The sign-file tool failed to build against libressl. Fix this by extending
the PKCS7 check and thus making sign-file link against libressl without an
error.
Signed-off-by: John Crispin <john@phrozen.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: David Howells <dhowells@redhat.com>

scripts/sign-file.c

@@ -41,7 +41,9 @@
  * signing with anything other than SHA1 - so we're stuck with that if such is
  * the case.
  */
-#if OPENSSL_VERSION_NUMBER < 0x10000000L || defined(OPENSSL_NO_CMS)
+#if defined(LIBRESSL_VERSION_NUMBER) || \
+	OPENSSL_VERSION_NUMBER < 0x10000000L || \
+	defined(OPENSSL_NO_CMS)
 #define USE_PKCS7
 #endif
 #ifndef USE_PKCS7