Add DEBUG_MODE as a conditional compile directive

Is your capability/feature request related to a problem?

With advent of some VHDL-2019 features, such as calling path, some vendors only make this available when the design has been compiled in a particular mode of theirs - such as debug mode.

In addition, it would be nice if open source libraries could add extended debug information when debug mode is active.

Describe the solution you'd like

Add conditional compile directive and corresponding VHDL function call that indicate whether DEBUG_MODE is on or not.

This way libraries can add extended debugging information when in debug mode such as get_call_path or other when in debug mode.

Describe alternatives you've considered

Nothing I can think of currently.