patch pki_gcrypt.c to be compilable without CMake

src/pki_gcrypt.c

@@ -24,6 +24,8 @@
 
 #include "config.h"
 
+#ifdef HAVE_LIBGCRYPT
+
 #include <string.h>
 #include <stdlib.h>
 #include <gcrypt.h>
@@ -1672,4 +1674,6 @@ ssh_signature pki_do_sign_sessionid(const ssh_key key,
 }
 #endif /* WITH_SERVER */
 
+#endif /* HAVE_LIBGCRYPT */
+
 /* vim: set ts=4 sw=4 et cindent: */