Qt Crator UI does not update when CMake build gets cancelled

When a CMake build is cancelled e.g. by the "stop" button, CMake gets terminated but this is not reflected in the UI:

• the button stays a stop button rather than turning into a build button
• the compile output pane does not show the usual "cmake terminated" message
• QtCreator asks for confirmation of cancelling the build when closing, even though CMake already got terminated

A similar bug happened when running a debug session with GDB.

The bug happens since 5.0.1 but is not present in 5.0.0. More precisely, it happens since commit ebae255e49cd2c5411f6948417e0d927dd020525.