ifdef Q_?S_* cleanup

- clear up some Q_OS_LINUX vs. Q_OS_UNIX
- clear up Q_WS_* vs. Q_OS_* (relatively theoretical exercise)
- use proper #if-#else cascades instead of free-standing #ifs

src/plugins/debugger/debuggerplugin.cpp

@@ -112,7 +112,7 @@ const char * const BREAK_BY_FUNCTION    = "Debugger.BreakByFunction";
 const char * const BREAK_AT_MAIN        = "Debugger.BreakAtMain";
 const char * const ADD_TO_WATCH         = "Debugger.AddToWatch";
 
-#ifdef Q_OS_MAC
+#ifdef Q_WS_MAC
 const char * const INTERRUPT_KEY            = "Shift+F5";
 const char * const RESET_KEY                = "Ctrl+Shift+F5";
 const char * const STEP_KEY                 = "F7";
@@ -1136,7 +1136,7 @@ void DebuggerPlugin::readSettings()
     DebuggerSettings::instance()->readSettings(s);
 
     QString defaultCommand("gdb");
-#if defined(Q_OS_WIN32)
+#ifdef Q_OS_WIN
     defaultCommand.append(".exe");
 #endif
     //QString defaultScript = ICore::instance()->resourcePath() +