Avoid warning on empty expressions

For some reason, Q_UNUSED includes already a semicolon, adding one
on the user side creates an additional empty statement.

Change-Id: I9c5e8fac381345a60792cb75e2938fd53958d3b0
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/valgrind/memchecktool.cpp

@@ -818,7 +818,7 @@ void MemcheckToolPrivate::heobAction()
     // process environment
     QByteArray env;
     void *envPtr = nullptr;
-    Q_UNUSED(envPtr);
+    Q_UNUSED(envPtr)
     if (!envStrings.isEmpty()) {
         uint pos = 0;
         for (const QString &par : envStrings) {