Change libresourceqt's .pc file.

The one public port of this library to Qt 5 changed the .pc to libresourceqt5,
to avoid clashing with the Qt 4 version.

Change-Id: I6a248606e20c4e7a8f432612ca00aded846264d9
Reviewed-by: Andy Nichols <andy.nichols@digia.com>