iftop: ignore additional warnings (#27601)

fixes part of: #26522

iftop.yaml

@@ -1,7 +1,7 @@
 package:
   name: iftop
   version: 0.17
-  epoch: 0
+  epoch: 1
   description: A tool to display bandwidth usage on an interface
   copyright:
     - license: GPL-2.0-or-later
@@ -16,6 +16,8 @@ environment:
       - ca-certificates-bundle
       - libpcap-dev
       - ncurses-dev
+  environment:
+    CFLAGS: "-Wno-unused-function -Wno-implicit-function-declaration"
 
 pipeline:
   - uses: fetch