Revert "Ninja: use absolute paths for sources and includes"

This reverts commit df7f1790b7cf69def45f55cb03ce0f9cef1eddb5.

It shows that absolute paths breaks dependency tracing and adds
lot of emtpy build commands.
Merge topic 'ninja-absolute-paths' into next

3030142 Revert "Ninja: use absolute paths for sources and includes"