gf180: fix access rights for klayout macro

[Scafir]

This fixes a regression introduced by 56ee4b0, which removed access rights to the pdk.

It is currently required for:

1. Saving the DRC (and soon LVS) options permanently
2. Holding the DRC default output directory

Fixes #273

[hpretl]

@Scafir Before merging this, we should discuss an alternative way. PDK locations should always be read-only, so if there is a file to be modified, it should be in user space. How difficult would it be to achieve this?

[Scafir]

I agree. This is not something I had in mind when I made my improvements in the PDK.
The DRC output directory requirement will be dropped when the new DRC approach is merged, which should hopefully be soon.

For the DRC/LVS options, I am not sure how to implement a solution that is cross-plateform compatible. I will think about this, but it cannot be too hard.

I will also need to make sure write access is not required elsewhere (e.g: xschem LVS netlist to klayout conversion).

[hpretl]

@Scafir Exactly. What can be safely used is

• $HOME for user settings
• /tmp for temporary stuff
• $DESIGNS for project-related settings. In this sense DRC/LVS settings should go to $DESIGNS, which is the /foss/designs tree