They affect all targets and make it more difficult to control the order
of the includes at a later stage.
Refs #0

Avoids need to set different paths for IDEs
Refs #20381

Refs #20381

Windows needs the DLLs and executables to be in the same directory
or it can't find the dependencies. This can be solved if running through
a wrapper script but the IDE calls th .exe directly and not allowing
this would degrade the developer experience alot.
This only affects the developer build and not the installed locations.
Refs #20288

Refs #20288

Refs #20288

The Qt4/Qt5 plugins cannot be loaded into the same process so
need to be separated at build time.
Refs #20288

git describe requires a tag to be present in the tree and in particular
errors out if a shallow clone is used. We no longer use the number of
commits after the last tag as a descriptor so "git log" will suffice.

The version of Python used is then completely controlled by the
-DPYTHON_EXECUTABLE cmake option.