Fix warning
Fix warning

Warnings came up using MinGW 4.4:
* qmakebuiltins.cpp: 'QString windowsErrorCode()' defined but not used
[...]

Change-Id: I80827f7f740ff380f13cef96d6b43baaa7e179cb
Reviewed-by: Orgad Shaneh <2b010cbad792a0c0a8175f752f93f83941fc6bc1@gmail.com>
Reviewed-by: Joerg Bornemann <47777b9406dbddd02a3fdca8341789a013805a11@digia.com>
(cherry picked from qtbase/81f4ecdd7920ffcec4244bf70a0aedf4fbfb66e3,
 (cherry picked from qtcreator/0e13cf3faffc7463ae2bf535dfdb008202112cc4))
Reviewed-by: hjk <f81b91af79013637d070c18d38a75b90eaae8ba3@nokiamail.com>
Reviewed-by: Oswald Buddenhagen <6a8868beda3e139b5ac22b2534a23d3e6ba81819@digia.com>

mer-qt/qttools,mer-qt/qttools,mer-qt/qttools,mer-qt/qttools,mer-qt/qttools,mer-qt/qttools