build: Disable `unneeded-internal-declaration` warning

Change-Id: I48c99d7a1c224faebc63339d40f700a9a675d2da
Refs: #1588
diff --git a/.waf-tools/default-compiler-flags.py b/.waf-tools/default-compiler-flags.py
index 0df0347..af237f5 100644
--- a/.waf-tools/default-compiler-flags.py
+++ b/.waf-tools/default-compiler-flags.py
@@ -21,7 +21,7 @@
     else:
         defaultFlags += ['-std=c++03']
 
-    defaultFlags += ['-pedantic', '-Wall', '-Wno-long-long']
+    defaultFlags += ['-pedantic', '-Wall', '-Wno-long-long', '-Wno-unneeded-internal-declaration']
 
     if conf.options.debug:
         conf.define('_DEBUG', 1)