[fpc-pascal] Prevent full unit path in ppu files? together with -Ur

[Martin]

When building packages for an installer, one uses -Ur.

Yet (on Windows) I noted, that the ppu contain the full path to the 
source file used to build that ppu.

Not a major issue, but slightly awkward.
- The files (ppu, and maybe sources) will be packed into an installer
- The end user installs them to a patch of their choice. This is most 
likely different from the build system.

In the best case, the end users system has now links to none existing files.
In the worst case, the links point to a different installation, with 
different versions of the files.

Well probably no harm, since fpc will not recompile those files.
Problematic maybe if other tools (like Lazarus) read that info from the ppu.

Therefore the question: Can that full path be prevented from getting 
into the ppu (or any other file)?