Add Q_FALLTHROUGH for Qt < 5.8

... and make use of it.
With gcc 7, the new option -Wimplicit-fallthrough is introduced and
added to the -Wextra set, triggering dozens of warnings in our sources.
Therefore, we annotate all obviously intended fall-throughs. The ones
that are still left are unclear and need to be checked by the respective
maintainer.

Change-Id: I44ead33cd42a4b41c28ee5fcb5a31db272710bbc
Reviewed-by: Nikita Baryshnikov <nib952051@gmail.com>
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/ios/iostoolhandler.cpp

@@ -33,6 +33,7 @@
 #include <coreplugin/icore.h>
 #include <utils/qtcassert.h>
 #include <utils/fileutils.h>
+#include <utils/qtcfallthrough.h>
 #include "utils/runextensions.h"
 #include "utils/synchronousprocess.h"
 
@@ -606,7 +607,7 @@ void IosDeviceToolHandlerPrivate::subprocessHasData()
         switch (state) {
         case NonStarted:
             qCWarning(toolHandlerLog) << "IosToolHandler unexpected state in subprocessHasData: NonStarted";
-            // pass
+            Q_FALLTHROUGH();
         case Starting:
         case StartedInferior:
             // read some data
@@ -771,7 +772,7 @@ void IosDeviceToolHandlerPrivate::stop(int errorCode)
     switch (oldState) {
     case NonStarted:
         qCWarning(toolHandlerLog) << "IosToolHandler::stop() when state was NonStarted";
-        // pass
+        Q_FALLTHROUGH();
     case Starting:
         switch (op){
         case OpNone:
@@ -786,7 +787,7 @@ void IosDeviceToolHandlerPrivate::stop(int errorCode)
         case OpDeviceInfo:
             break;
         }
-        // pass
+        Q_FALLTHROUGH();
     case StartedInferior:
     case XmlEndProcessed:
         toolExited(errorCode);