[Qt-creator] Project not linked when dependent .lib changes

[Robert Caldecott]

I have a unit test project that depends on a C++ project (all part of
the same 'workspace').  If I change a file in the .lib project and
build/run the unit test project it will correctly rebuild the .lib but
it _won't_ re-link!  I thought I was going mad earlier when my .lib
changes didn't appear to be showing up.  In order to make this work I
have to change one of the unit test files to force the linker into
action.  This sounds like a Qt Creator bug - I think that if a
dependent lib is rebuilt then the projects using it must be relinked.