Fix warnings in current debian-hardened CI.

We're getting "fallback annotation annotation in unreachable code"
warnings when we build with ALL_BUGS_ARE_FATAL. This patch fixes
that.

Fixes bug 40241.  Bugfix on 0.3.5.4-alpha.

src/core/or/channeltls.c

@@ -1225,8 +1225,9 @@ channel_tls_handle_var_cell(var_cell_t *var_cell, or_connection_t *conn)
        * the v2 and v3 handshakes. */
       /* But that should be happening any longer've disabled bufferevents. */
       tor_assert_nonfatal_unreached_once();
-
+#ifndef ALL_BUGS_ARE_FATAL
       FALLTHROUGH;
+#endif
     case OR_CONN_STATE_TLS_SERVER_RENEGOTIATING:
       if (!(command_allowed_before_handshake(var_cell->command))) {
         log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,

src/core/or/circuitlist.c

@@ -787,7 +787,9 @@ circuit_purpose_to_controller_hs_state_string(uint8_t purpose)
              "Unrecognized circuit purpose: %d",
              (int)purpose);
       tor_fragile_assert();
+#ifndef ALL_BUGS_ARE_FATAL
       FALLTHROUGH;
+#endif
 
     case CIRCUIT_PURPOSE_OR:
     case CIRCUIT_PURPOSE_C_GENERAL: