do not parse MSVC option /Gs as /GS

/Gs[size] will be added as additional option as there is no XML element
for this option.

Task-number: QTBUG-29329

Change-Id: I1f09bfdac90f9c5f2333dc03e6e4e6a206b4f6d0
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

qmake/generators/win32/msvc_objectmodel.cpp

@@ -603,9 +603,7 @@ bool VCCLCompilerTool::parseOption(const char* option)
             CallingConvention = callConventionFastCall;
             break;
         case 's':
-            // Warning: following [num] is not used,
-            // were should we put it?
-            BufferSecurityCheck = _True;
+            AdditionalOptions += option;
             break;
         case 'y':
             EnableFunctionLevelLinking = _True;