GUI: Reword the option for checking all #ifdefs.

The current wording was confusing (espcially related to CLI) since
it said the option will make Cppcheck to check all #ifdef configs.
But this really is case only when there is excessive amount of
those configs and without the option some would be ignored. So
format the option text in line of CLI switch and say it is forcing
not enabling checking of all configurations.

gui/settings.ui

@@ -7,7 +7,7 @@
     <x>0</x>
     <y>0</y>
     <width>589</width>
-    <height>281</height>
+    <height>313</height>
    </rect>
   </property>
   <property name="windowTitle">
@@ -135,7 +135,7 @@
        <item>
         <widget class="QCheckBox" name="mForce">
          <property name="text">
-          <string>Check all #ifdef configurations</string>
+          <string>Force checking all #ifdef configurations</string>
          </property>
         </widget>
        </item>