SDKtool: Make sure to use '/' as path separator

All internal paths in Qt Creator are using '/' as path separator.
Make sure to normalize paths set via the SDKtool to that convention.

Change-Id: If7ef250d49686a0f60d08516b718eb7c84a059ef
Reviewed-by: Tim Jenssen <tim.jenssen@theqtcompany.com>

src/tools/sdktool/addqtoperation.cpp

@@ -112,7 +112,7 @@ bool AddQtOperation::setArguments(const QStringList &args)
                 return false;
             }
             ++i; // skip next;
-            m_qmake = next;
+            m_qmake = QDir::fromNativeSeparators(next);
             continue;
         }