Fix qmake build in developer builds

When building with developer builds, all targets are built with
warnings as errors. In CMake this also applies to the qmake build.

Change-Id: Ie62681d6c4756c106f5931a2a7d452a18dfa45f1
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

src/corelib/io/qfilesystemiterator_unix.cpp

@@ -83,6 +83,8 @@ static bool checkNameDecodable(const char *d_name, qsizetype len)
     codec->toUnicode(d_name, len, &cs);
     return cs.invalidChars == 0 && cs.remainingChars == 0;
 #else
+    Q_UNUSED(d_name);
+    Q_UNUSED(len);
     // if we have no text codecs, then QString::fromLocal8Bit is fromLatin1
     return true;
 #endif