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

Signed-off-by: Felix Fietkau <nbd@nbd.name>

target/linux/generic/patches-4.4/211-sign-file-libressl.patch

+LibreSSL disables the CMS subsystem, so sign-file.c needs to fall back to using
+PKCS#7 in that case.
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+
+--- a/scripts/sign-file.c
++++ b/scripts/sign-file.c
+@@ -39,7 +39,7 @@
+  * signing with anything other than SHA1 - so we're stuck with that if such is
+  * the case.
+  */
+-#if OPENSSL_VERSION_NUMBER < 0x10000000L
++#if defined(LIBRESSL_VERSION_NUMBER) || OPENSSL_VERSION_NUMBER < 0x10000000L
+ #define USE_PKCS7
+ #endif
+ #ifndef USE_PKCS7