Add missing include
See https://bugs.gentoo.org/942814
> src/.../cli.h: error: uint8_t does not name a type
--- a/src/cli/cli.h
+++ b/src/cli/cli.h
@@ -8,6 +8,7 @@
 #define BOTAN_CLI_H_
 
 #include <botan/build.h>
+#include <cstdint>
 #include <functional>
 #include <ostream>
 #include <map>