Mac: Fix compilation warning

Change-Id: Ib2d388c468bd88d1774770585fbf8a64de7cfb53
Reviewed-on: http://codereview.qt.nokia.com/1831
Reviewed-by: Kai Koehne <kai.koehne@nokia.com>

src/libs/utils/environment.cpp

@@ -173,6 +173,7 @@ void Environment::prependOrSetPath(const QString &value)
 void Environment::prependOrSetLibrarySearchPath(const QString &value)
 {
 #ifdef Q_OS_MAC
+    Q_UNUSED(value);
     // we could set DYLD_LIBRARY_PATH on Mac but it is unnecessary in practice
 #elif defined(Q_OS_WIN)
     const QChar sep = QLatin1Char(';');