Do this by tracking CMAKE_CURRENT_{SOURCE,BINARY}_DIR variables.
This is achieved by injecting CMake code with CMAKE_PROJECT_INCLUDE
and overriding some builtin functions with a wrapper that adds
additional trace information.
This PR refactors the old output_target_map, which was a
raw dict, into it's own class. This makes the access to
the map more uniform and robust (at the cost of more lines
of code).
Additionally relative paths to the build directory are
now also tracked for outputs. This is neccessary to
corretcly distingluish files with the same name, that are
in different directories.
Daniel Mensinger
Xavier Claessens
Wolfgang Stöggl